This paper investigated the impact of seasoned equity offerings (SEO) on stock return of listedcompanies in Ho Chi Minh City market using the method “event study” which has been basicallyformed by Campbell, Lo, and MacKinlay (1997). The sample includes 332 SEOs from 2007 to 2010.The main findings show evidence that the Ho Chi Minh City market was not efficient in terms of thesemi-strong form because the price has increased significantly on the ex-right date, day 0. In an oppositeway, the market also reacted significantly negatively from T-4 to T-2. There are some significantimpacts of timing on issue methods – equity right issues were in priority for favorable time and issuesas “dividend by stocks” were chosen during unfavorable time.