Along with the growth of Taiwan¡¦s capital markets, the public tend to serve stocks as the main investment tool. Underwriting markets are also monitored by investors. Generally, Taiwanese firms¡¦ stocks possess ¡§honeymoon periods¡¨ after they went public, in which the stocks kept gaining prices for consecutive days. Due to the phenomenon, companies tend to went public once the requirements are satisfied. On the other hand, investors are willing to purchase such stocks, thus let the underwriting market prosper. The aspect of initial public offerings (IPOs) is also gaining attention of researchers. This research aims at examining the relation between Taiwanese firms¡¦ IPOs¡¦ initial return and the Monday effect and Intra-month effect. This thesis also tried to discover that whether Taiwanese IPOs possess differences between size and industry groups. The results indicate that Taiwanese IPOs have lower return if issued in Mondays, which is the Monday effect. The reason may be that the closed market in weekends allowed investors to spend more time to search and to analyze information and to hinder themselves from overreaction. In addition, when issuing companies are determining underwriting prices, they tend to serve discount as a risk compensation for the uninformed investors, thus when investors have more time to analyze their investment decisions, the issuing companies need not to discount to induce investors.