Investors and researchers have been paying increasing attention to the emerging stock markets. In this research we study whether or not weak-form efficiency, which is relatively popular in emerging stock markets, holds for the Vietnamese stock market. We check the random walk hypothesis for weekly stock market returns employing three statistical techniques namely autocorrelation test, variance ratio test, and runs test. Data for analysis was collected from July 28th2000 (the first trading session) to July 28th 2013 (13 years of market operation). Through the graph showing movements in daily prices of the chosen representative stocks and the Vietnam stock index (VN-Index), it is visual that the Vietnamese stock market is not efficient; the fact that psychological factors strongly influence investors is among elements making stock prices predictable. Estimated results have strongly rejected the random walk hypothesis for the whole period of the samples and for the first two cycles of the market (except for the third cycle). Particularly results from the third cycle of the Vietnamese stock market alone (from February 24th 2009 to July 28th 2013) have provided evidence supporting random walk hypothesis in VN-index. It shows the fact that the efficiency of the Vietnamese stock market has gradually been improved during nearly 10 years in operation. The main conclusion drawn from results of this research is that it may be the case that the weak-form efficient market hypothesis does not hold for the Vietnamese stock market.
