This study empirically examined the effects of firm-specific factors and market-specific factors on the business performance of Korean overseas subsidiaries in China and North America, with a focus on market orientation as the key determinant. The results revealed that while some variables were significant for Korean firms in both the Chinese and North American markets, other variables showed different results across the two markets. In the Chinese market, business performance of overseas subsidiaries improved as market orientation increased and competition decreased. Additionally, differentiation advantage was found to influence market orientation and enhance business performance. This implies that in developing country markets, where Korean firms possess brand competitiveness, companies with higher differentiation advantage rather than cost advantage exhibit higher market orientation and consequently achieve better business performance. In the North American market, similar to the Chinese market, higher local market orientation of subsidiaries led to better business performance. Furthermore, for overseas subsidiaries in North America, business performance improved as firms had greater international experience, larger firm size, higher market growth, and lower competition. In the North American market, due to the still-negative country-of-origin effect toward Korean products and low brand competitiveness, firms with higher cost advantage demonstrated higher market orientation and better business performance. Combining the results from both the Chinese and North American markets, business performance of Korean firms' local subsidiaries improved as market orientation increased. Moreover, while market growth and competitive intensity affected the business performance of overseas subsidiaries, their impact was relatively smaller compared to that of market orientation. This indicates that even if the local market exhibits high growth potential and weak competitive intensity, the performance of overseas subsidiaries cannot improve unless the firm is market-oriented.