Although it is an important building block of regional integration, very little research has investigated border trade between neighboring countries. This paper fills this gap by examining the patterns and determinants of China's border trade with its neighboring countries. First, a disaggregated, firm-product level trade data is used to provide a detailed overview of border trade growth and dynamics. The paper shows that trade liberalization has significantly encouraged new firms to enter the export market, and new private firms account for the majority of the expansion in border exports and the shift toward more sophisticated products. Second, a gravity model is used to investigate the determinants of border trade. The results suggest that multilateral and regional integration, market size and institutional quality play important roles in promoting border trade.