The purpose of this research is to examine whether the optimal portfolio formation and selection model uses two methods, namely, a single index model and a constant correlation model to offer better investment choices for investors. The selected sample is 46 part companies from Kompas 100 listed on the Indonesia Stock Exchange. The daily closing price of 46 sample shares from February 2014 to July 2018 is considered for calculating return and risk of shares, while the IDX is used as a proxy for market indexes.