This article examines 57 companies listed on the Ho Chi Minh City Stock Exchange from January 1, 2015 to March 31, 2020, to check whether or not investors' sentiment impacts the return of these stocks. Investor's daily sentiment towards each stock was measured by the psychological line index. The results of the study using both regression methods, Fama-MacBeth and General Least Squares, show that the influence of investor sentiment to return stocks in the stock market was significant and could not be ignored. Besides, the psychological factor of investors, their trading behavior causing stock supply-demand imbalance were all important factors affecting stock return. The study also found that the effect of firm size on stock returns was more pronounced when both investor sentiment and behavior were used in research models. The finding from this study suggests that individual investors who trade stocks every day can use psychological line index, which is one of the groups of decision-making indicators.