The purpose of this paper is to investigate behavioral patterns expressed by investors in the Thailand stock market. The paper examines investment decision-making processes in the context of the current financial market in Thailand to shed some light on behavioral-induced pattern behind such investments. Data for this research was collated from 8 individual investors by semi-structured and in-depth interview. There are four behavioral factors of individual investors in Thailand Stock Exchange: Overconfidence, Excessive Optimism, Psychology of risk, and Herding Behavior. Securities Companies may also use the findings of this research for better understanding on investors’ decision to give better recommendations to them. Stock prices then reflect their true value and Thailand stock market becomes the yardstick of the economy’s wealth and helps enterprises to raise capital for business activities.