In the stock market, investors are regarded as rational being, but during the different market conditions, investors tend to react in an irrational manner which could lead to loss of investment. This prompted the investigation into the relationship between stock market conditions and investors' reaction in Nigerian stock market. Primary data was used to investigate investors' reaction towards stock market conditions and the data were sourced via a structured questionnaire from two hundred and twenty-one (221) registered dealing members in Lagos State, out of which only one hundred and seventyeight (178) responded. The study employed descriptive statistics to analyse the responses from the questionnaire, while Chisquare (χ 2) was used to determine if stock market conditions had any relationship with investors' reactions. The results of the study showed that there is a relationship between stock market conditions and investors' reactions in Nigerian stock market. This implied that when the different market conditions occurred, they influenced investors' decision on whether to buy, sell or hold on to a stock. The study therefore recommended that the influence of market conditions on investors' reactions should be put in check by investors because immediate reaction to every conditions that affect the market could lead to massive loss of investments.