This study examines whether a shift in the trade structure affects China–South Korea relations. Bilateral trade between the two states has flourished since the normalization of diplomatic relations in 1992. South Korea leveraged its comparative advantage by exporting high-technology goods to China, while China exported labor-intensive goods to South Korea. However, as China advanced technologically and began to rival South Korea in the 2010s, the trade structure shifted toward reduced complementarity. China began producing high-tech and intermediate goods domestically, leading to a decline in South Korea’s exports to China. Meanwhile, South Korea continued to import raw materials and minerals from China, resulting in a decrease in South Korea’s trade surplus with China. Although a shifting trade structure may not be the sole factor, the two states also started experiencing various diplomatic conflicts resulting from North Korea’s provocations, South Korea’s alignment with the U.S., and the intensifying U.S.–China rivalry. Within this context, the author conducted a statistical analysis to investigate whether declining trade complementarity is associated with changes in China and South Korea’s stance toward each other, mainly from South Korea’s perspective. The analysis reveals that a decline in South Korea’s trade complementarity with China—and China’s diminishing reliance on imports from South Korea —negatively influences its stance toward China. Likewise, as China’s export profile increasingly matches South Korea’s import profile—and as China exports more to South Korea—China’s stance toward South Korea is also negatively affected. The findings suggest that trade may have limited power in mitigating China–South Korea conflicts in the future.