Traditionally human resource functions are performed in house, but recently the subject on outsourcing human resources is becoming more and more popular. According to an article published in 2004 by the INC. 500 magazine, 18 human resource service providers were chosen to be the most fast growing corporation in the US, in the mean time the Fortune 500 and Forbes 500 corporations listings both had human resource business process outsourcing firms listed inside. This research focuses on successful human resource service providers in Taiwan, the main objective will be finding out what current environment are they facing and what kinds of corporate resources do they possess to cope with their business operational needs. Using these findings as the basis, we employ the Transaction Cost Theory to do further analyze in their competitive and strategy model. Further more, by applying these strategies what economical profit can the service provider bring to there customers. In this research, we use a case study approach and employ the in-depth interview technique which includes five global human resource service provider¡¦s Taiwan branch as are research sample. Moreover, by using domestic and international references as auxiliaries, we can draw out the business model of the human resource service providers. The inference of this thesis is that corporate resources and brand can decrease the transaction cost triggered by outsourcing activities, and by decreasing transaction cost the service providers can establish trusting and cooperative relationships more successfully. When trusting relationships are in place, service providers can deliver more added value and economic profits based on their originally service content. Last but not least, by absorbing the feedback from satisfied customers, human resource service providers can accumulate solid professional knowledge and increase brand value.