Firms pay cash dividends to reduce the agency costs, and then insider stock ownership affects the dicision of dividend payout ratio. In this study, it is tested that firm's insider stock ownership affects the decision of dividend payout ratio, but the relation between dividend payout ratio and insider stock ownership is nonmonostic. The empirical evidence shows that at low levels of insider stock ownership, increase in the percentage of stock held by insiders decreases dividend payout ratio, but beyond the point of entrenchment increase in the percentage of stock held by insiders increases dividend payout ratio. Thus, the dividend payout ratio and the percentage of stock held by insiders are in a parabolic relation. This implies that there may be a optimal insider stock ownership In lead to the minimun dividend payout ratio.