As Taiwanese performing arts environment changes, some performing arts groups begin to co-operate with business companies and share marketing resources aggressively. On the other hand, since National Culture and Arts Foundation has launched Performing Arts Marketing Platform project in 2006, which has promoted several platforms to co-market with business companies and to gain benefits. However, this business model has not been developed throughly. The purposes of this study are to explore the theories of co-marketing alliances; to understand the influence of the marketing platforms during co-marketing alliances as arts intermediaries; to compare four cases of co-marketing alliances; to modify the co-marketing alliances models and to conclude some suggestions for business companies and Performing Arts Marketing Platforms to improve their cooperation. This study is based on four co-marketing alliances case studies, with observation and in-deep interviews to collect research data. The study concludes that except marketing concern and brand awareness, social responsibility, which helps performing arts organizations to gain more trusts from business companies, becomes another important motivation to form alliances. These motivations affect business companies for choosing their partners, managing the alliances, and evaluating the results. Furthermore, ¡§complementary possibilities¡¨ and ¡§alliance promoters¡¨ are two advantages for Performing Arts Marketing Platforms to built relationships with business companies. Since customers¡¦ cognitions and attitude are not easy to be evaluated, business companies can only measure the outcomes of the alliances through number of consumers, advertisement impression, overall revenue and return questionnaires, which are also difficult to distinguish from normal situations. Therefore, most of the business companies prefer to evaluate the alliance by managers¡¦ subjective judgments. In order to establish a steady alliance, a business company has to familiar with the diversity of performing arts and alternative alliance models beforehand. A Performing Arts Marketing Platform has to consider the needs of business companies, performing arts organizations and itself. The study also suggests a Performing Arts Marketing Platform should increase its advantages and emphasize equal partnerships. It can connect the resource from all the performing arts organizations it helps, and enhance alliance promoter¡¦s professional ability.