International R&D collaboration is perceived as important R&D strategy to obtain complementary resources, learn from the partner as well as sharing risks and costs. Previous studies suggested that international R&D collaboration has positive impact but the impact investigated in literature are either not clearly defined or largely focused on business or technological impact. This study attempts to investigate social and legal impacts of international R&D collaboration by analyzing East Asian collaborative patents with multiple assignee countries from the perspectives of social network theory as well as cross-border patent infringement probability. It is found that international R&D collaboration has positive influence on both social and legal impacts. The evolving pattern shows that China and Taiwan are the most prolific and fastest-growing patenting countries. Also, Taiwan is the most important partner country in East Asia's internationalization of R&D. Two important contributions of this study can be summarized as follows: 1) this study defines social and legal impacts based on which the dynamics of East Asia's international R&D collaboration can be obtained, 2) the legal impact defined in this study can be used to evaluate patent value as well as evaluate the quality of R&D partnership in East Asia.