A substantial body of research has examined the customer-supplier relationship in Korea from both the economic and social perspectives. The majority of the Korean studies on the customer-supplier relationship have focused on the performance of the suppliers of large companies (Chung, 2007; Shim, 2011; Kim and Shin, 2015). In this study, we extend this line of research by investigating the effect of the customer-supplier relationship on the cash holdings of the supplier firms. The customer-supplier relationship can directly affect a firm's cash flow, which in turn can significantly affect the supplier firm's working capital management, sales expenditures (Kalwani and Narayandas, 1995), leverage (Titman and Wessels, 1988; Kale and Shahrur, 2007; Banerjee, Dasgupta, and Kim, 2008), cost of debt (Campello and Gao, 2014; Cen, Dasgupta, Elkamhi, and Pungaliya, 2015), and cost of equity (Dhaliwal, Judd, Serfling, and Shaikh, 2016). Firms hold cash as a buffer to protect themselves from adverse cash flow shocks. If a customer accounts for a large proportion of a supplier's sales, then the loss of that customer will result in a large adverse cash flow shock. As a precaution against the additional operating risk associated with having an important relationship with a customer, suppliers tend to hold cash in proportion to the importance of the customer-supplier relationship (Itzkowitz, 2013). Bae and Wang (2015) find that the relationship-specific investments of firms in customersupplier relationships are associated with the high cash holdings of the supplier firms. Firms that rely on relationship-specific investments tend to maintain high cash reserves as a cushion to sustain their relationship-specific investments when negative shocks occur (Titman, 1984). Using R&D based measures and durable-goods industries as proxies for the extent of relationship-specific investment, Bae and Wang show that the positive relationship is more pronounced for firms with positive R&D expenses and firms in the durable-goods sector. Kim, Jinn, and Han (2012) find that the leverage of Korean firms is negatively related to the R&D intensity of their suppliers and customers on the industry level but not the firm level. The primary goal of this study is to determine how the customer-supplier relationship affects the suppliers' cash holdings. We use the percentage of sales to major customers and the major customer concentration to measure the customer-supplier relationship. Firms' sales data from 2006 to 2012, including the proportion of sales and the customer names obtained at the firm level from Korea Enterprise Data (KED), are used to calculate the customer-supplier relationship variables. As a supplier's dependence on major customers increases, the suppliers can potentially lose a significant proportion of sales, which could cripple their financial health. Therefore, the suppliers are likely to hold additional cash to protect themselves against the operating risk induced by their buyers. Our results indicate that suppliers are motivated to increase their cash holdings as a precautionary measure. This positive relationship between a supplier's cash holdings and the supplier's reliance on customers is also found in Korean supplier firms. The suppliers of customers that have considerable bargaining power may face higher uncertainty of keeping their contracts. In the case of big customers, such as leading companies, the suppliers face a higher risk of losing sales. Therefore, the suppliers of leading companies have an incentive to hold more cash as a precaution. Accordingly, the results of this study indicate that the positive relation between customer–supplier relationships and cash holdings is more pronounced for firms with big customers. Following Bae and Wang (2015), the sample is divided into subsamples based on a measure of relationship-specific investments that uses firm level R&D intensity as a proxy for relationship-specific investment. The results indicate that firms with more relationship-specific investments hold more cash than other firms. Research suggests that the precautionary motive is stronger during recession periods when firms have less access to credit and their customers are more likely to cancel purchases (Ikowitz, 2013). In line with this, the findings of this study show that during the 2008 and 2009 financial crisis, suppliers held more cash relative to the strength of their relationships than during other periods.Although the results of this study show that a supplier's reliance on major customers induces the supplier to hold more cash, the customers may prefer to deal with financially stable suppliers and thus purchase more from such suppliers. To handle this endogeneity problem, a two-stage least squares (2SLS) regression is conducted in which the instrumental variable is a dummy variable that is set to one if a supplier is located in the same area with one or more customers, and zero otherwise. The results show that although the instrumental variable is associated with the proportion of a supplier's sales, the relationship does not affect the firm's cash holdings. Thus, the 2SLS analysis supports the main results of this study.