The effect of customer concentration on the cash holding level, accounts receivable level, the Inventory level and the level of fixed assets of the companies will be investigated. Research data has been collected using the information of 150 companies from the stock market of Iran in a period of 7 years (i.e. from the fiscal year 2017 to 2023). The findings of the research show that in the stock market of Iran, the concentration of customers on the cash holding level, the level of accounts receivable and the level of fixed assets has a significant positive effect and Customer concentration has a significant negative effect on the inventory level. In fact, based on the results of research in companies with a high level of customer concentration, because of the risk of selling to major customers, companies tend to keep more cash. Due to the fact that companies tend to maintain major customers, they usually agree to grant credit (credit sales) to major customers, the level of accounts receivable increases with the increase in the concentration of customers. With the increasing level of customer concentration, companies tend to invest in fixed assets to develop the company's line to produce according to the order of these customers. Due to the fact that sales to major customers are usually done through the conclusion of contracts, the company will have the ability to have a more appropriate management of the cycle of supply and consumption of goods inventory.