The current study examines the Stock Market Anomalies in Colombo Stock Exchange (CSE); Sri Lanka during the period of 2004 to 2013. The existences of both Day of the Week Effect and Monthly Effect have been tested using daily and monthly data respectively. The Ordinary Least Squares (OLS) method and GARCH (1, 1) model were employed to capture the Day of the Week effects and Monthly Effects along with the daily volatility behavior. The sample period was divided in to two periods as War Period and Post War Period in order to take the impacts of the War in to account. The results indicate the presence of negative Monday effect and the positive effects for all other days only for the war period. Further, the positive volatility effect on Monday and the negative volatility effect on Friday have been examined for both war period and the entire sample period with significant Wald F statistics. Despite, the positive January effects are common for all sample periods, the negative December effects cannot be identified for post war period. Hence, the study confirms the existence of Stock Market anomalies; both day of the week effect and monthly effect particularly during the war period. Moreover, these seasonality patterns limit the validity of Efficient Market Hypothesis in the context of Colombo Stock Exchange.Keywords: day of the week effect, monthly effect, efficient market hypothesis, volatility effect, stock market anomalies