Objective - The objective of this study is to investigate how institutional ownership and firm size affect firm value. The study also investigates the moderating effect of tax avoidance on the relationship between institutional ownership and the size of a firm on its value. Methodology/Technique - A model was developed and tested using a sample of 66 manufacturing companies listed on the Indonesian Stock Exchange between 2012 and 2014. Findings - The data was collected and analysed using a least square regression and moderated regression analysis. The analysis shows that institutional ownership and firm size affect firm value. The results also indicate that tax avoidance moderates the effect of institutional ownership and that of a firm's size on its value. Type of Paper - Empirical Keywords: Institutional Ownership, Firm Size, Tax Avoidance, Firm Value. JEL Classification: G30, G32, G39.