This paper presents an empirical study of the effect of mergers and acquisitions on the return of shares of acquirer and target fi rm. For this research, we have taken all listed companies of BSE for which merger and acquisition has taken place between 2000 and 2010. Total 80 samples are taken, among this 40 are of mergers involving 20 of acquirer and 20 of target fi rms, and 40 of acquisition involving 20 of acquirer and 20 of target fi rms. A comparative analysis of abnormal gains of target fi rms involved in M & A reveals that the abnormal gains of target fi rms of acquisition was higher than target fi rms of merger. In the context of news leakage of information, it can be suggested that the investment strategies involving buying shares of target fi rms prior to the announcement of a merger and selling them off after the merger announcement could result in profi table opportunities. Keywords: Mergers and Acquisitions, Target fi rms, Acquirer fi rms, Abnormal gains.