This study aims to an examine the empirical evidence the effect of the investment opportunity set and earning persistence on earning quality with firm size as moderating variable. The population used in this study are manufacturing companies listed on Indonesia Stock Exchange during 2014 until 2016. Sampling method that use is purposive sampling. The number of samples in this study are 102 samples. Types of data us is secondary data obtained from www.idx.co.id. Analysis technique used were multiple regression analysis by SPSS 15.0. The result showed that investment opportunity set and earning persistence no effect the earnings quality. Firm size as the moderating variable have no influence between investment opportunity set and earning persistence with earnings quality.