This paper attempts to examine how conservatism, overconfidence, herding behavior and availability bias influence investors’ investment decisions in Nepalese stock market.The research methodology is quantitative, with a questionnaire created and disseminated to a sample of 384 individual investors in Nepal's stock market. SPSS software was used to examine the data and determine the direct effects of the hypotheses. Descriptive and causal-comparative research design utilized with Mann-Whitney U Tests, Kruskal Wallis H Test, correlation, and regression analyses. Beta coefficients indicate higher positive influence of Conservatism on Investor’s Decision Making. This study found that overconfidence, Conservatism, Herding behavior and Availability bias have different degrees of impact on investment decisions. It is suggested that this study will increase investors' awareness of how psychological aspects affect their stock market decision-making, leading to more rational investments and improved market efficiency.