The objective of this study is to examine the differentiated influence of sell-side advisors and buy-side advisors on mergers and acquisitions (M&A). Unlike prior studies on M&A advisors, the study addresses different roles of target and acquirer advisors, and explores their influences on the cumulative abnormal returns (CAR) and acquisition premiums with an empirical analysis of longitudinal data of M&As conducted by Japanese listed firms except financial companies from 1995 to 2012. M&A data were obtained from the Securities Data Corporation’s (SDC) database, and the individual firm data were collected from the Nikkei Economic Electronic Databank System (NEEDS), which provides a wide range of corporate information including financial status, operational performance, and strategy. Using a sample of 452 cases for the CAR and 498 cases for the analysis of acquisition premiums, the empirical results support the hypotheses of the target advisor’s positive association with CAR and acquirer advisor’s positive association with acquisition premiums. The findings of this study indicate the target advisor’s positive contribution to the success of acquisition process and performance, and acquirer advisor’s negative influence on the deal progress. The study provides theoretical implications on M&A research and practical insights into the investment banking industry.