The traditional notion of stock market's participants behavior to maximize their expected utility with perfect control in financial decisions is becoming less popular due to the emergence of a new field, Behavioral finance, which suggests that sometimes emotions and psyche influence the investors' decisions causing them to behave in irrational ways. Behavioral finance explains that investors fall prey to certain cognitive biases and make sub optimal decisions. More ever it is suggested that personality plays an important role in determining the behavior of investors. Thus the purpose of this study was to determine the relationship between investor?s personality traits and cognitive biases. To achieve this purpose, survey methodology was used and a questionnaire was distributors among 200 randomly selected investors in Lahore Stock Exchange (LSE). Findings showed that a significant number of investors were exposed to Overconfidence, Mental accounting and Confirmation bias. The results also showed that there is a positive relationship between overconfidence and agreeableness, extroversion, consciousness and there is negative relationship between overconfidence and neuroticism.