The emergence of the Covid-19 Pandemic has made the Indonesian stock market unstable. Investment behavior in a person can change at an unknown time. By incorporating planned behavior theory and perceived risk theory, this research analyzed the change of investment behavior from six different variables. Therefore, the purpose of this research is to compare the investors' behavior before and during Covid-19 Pandemic in Indonesia Stock Market. Those are investor's attitudes, subjective norms, perceived behavioral, perceived risk, behavioral intention, and actual behavior before and during the Covid-19 pandemic in Indonesia Stock Market. The data was analyzed using the paired sample t-test. The results stated that investor's investment behavior significantly changes in a period of before Covid-19 Pandemic and during Covid-19 Pandemic. It happened because of any information obtained about the instability of the current stock market, the influence of people around who began to reduce investment activity in the stock market, a lack of self-control in an individual, and a greater risk of losing money.