Abstract: The ultimate aim of this study is to investigate the impact of behavioural biases on the stock investment decision of individual investors at Bahrain Bourse by exploring the biases, specifically overconfidence, loss aversion, herding, and risk perception, and identifying their effect on investment decision making. To conduct this study, a number of questionnaires were distributed to the participants using the snowball sampling method. A sample of the questionnaire was randomly distributed to individual investors in Bahrain Bourse, asking them to distribute the questionnaire to their partners or relatives who are potential investors. Consequently, 168 responses were collected and analyzed using the IBM SPSS statistics software and Microsoft excel. Descriptive statistical analysis methods were also used on the collected data. To test the hypotheses and determine the impact of each chosen variable on investment decision- making; correlation analysis and regression analysis methods were used in this study. As a result, a statistically significant positive correlation was found between all behavioural biases of the study and the individual's investment decision making in Bahrain. Multiple regression results showed that all independent variables were found to have a statistically significant positive effect on investment decision making. This confirms the importance of behavioural biases' impact on individual's investment decisions. Investors can be aware and in control of these biases when they make their investment decision in the market. Keywords: behavioural finance, investment decisions, individual investors, Bahrain Bourse.