The purpose of this study is to determine whether the support of top management significantly improves the level of environmental collaboration with participating companies upstream and downstream of the green supply chain and the impact on environmental performance. The results of the empirical analysis of 301 companies that are establishing a green supply chain are as follows. First, top management’s support positively affects the level of collaboration with suppliers and customers in the green supply chain. Secondly, support from top management has a direct impact on the company’s environmental performance. Thirdly, the environmental collaboration of participating companies partially plays a mediation role between the support of top management and the environmental performance. This study has significance in that it analyzes the theoretical mechanism of top management’s support for environmental collaboration with participating companies, leading to environmental performance, and draws implications.