Maintaining online services of high quality has become a crucial factor for brokerages to gain competitive advantages. Because of the attributes of the product uniformity of online trading, online brokerages have grown significantly with IT development, since the early 2000s. Now, as the online trading business gets mature, the profitability of the IT investment and the quality of IT-based services became questioned. This study examines the issues of IT investment and its contribution by analyzing the relationship between the quality of online service and IT investment. In addition, it also investigates the relationship of the quality of online services and profitability of brokerage. Our results show that IT investment draws cubic-style, curvilinear relationship with the service quality of online trading and only high quality services can lead to the increase of profitability.