: The Stock Portfolio Performance Based on Undervalued and Overvalued Using Capital AssetPricing Model. The purposes of this research are investigating the stock portfolio performance basedon undervalued and overvalued using Capital Asset Pricing Model. The sample used in this research isthe go-public companies whose stocks are listed at LQ 45 Index Februari - Juli 2014 period in IndonesianStock Exchange. The sample selection is done by purposive sampling method, analyzed using TreynorIndex and tested by mean difference statistical test. The result of this research show that there is nosignificant difference between undervalued stock portfolio performance in the forming period and thefollowing period, the performance of forming period is decreasing in the next period. Overvalued stockportfolio performance in the forming period has no significant difference with the following period andthe performance of forming period is increasing in the next period.