This paper analyzes the effect of product market competition on controlling family’s voting rights and cash flow rights for member firms in business groups. Empirically, we confirm that member firms in competitive market have lower discrepancy, lower ownership of affiliates, and higher controlling family’s direct ownership than those in non-competitive market. This result means that product market competition disciplines controlling family on arranging the optimal ownership structure to maximize the shareholder value. On the other hand, such disciplinary effects of product market competition is mainly observed in member firms with lower market share in their own industry, in member firms of older business years, and in non-listed member firms.