Regarding the critical role of liquidity in asset price discovery, sharing of financial risk and transaction costs reduction, it is important to know about the effective factors. This study offers evidences about the role of institutional ownership in the stock liquidity. In this research, for separating various impacts of institutional ownership, we used two measures as institutional ownership level and concentration. The level of institutional ownership is the proxy of trading and monitoring activity and the concentration of such ownership is the proxy of adverse selection and free float share reduction. We defined 15 different trading and information liquidity measures. Considering sampling limitations, we examined 138 corporations, from 1384 to 1388. We utilized linear multivariable regression to test our research hypothesis. The results indicate that liquidity is positively related to institutional ownership level; but institutional ownership concentration has a significant negative effect on stock liquidity. The finding is true about both trading measures including trading volume, free float share percentage and Amihud measure and also information measures like bid-ask spread.