This paper explores the relationship between socioeconomic status (SES) and the recent rapid decline in marriage rates in China and South Korea, using nationally representative longitudinal data. The analysis shows that recently rising never-married rates (NVMR) are increasingly concentrated among lower-SES individuals, especially in highly urbanised areas in both countries, highlighting the growing significance of financial barriers to family formation in recent years. Furthermore, income has become a stronger predictor of marriage entry by men in both nations. The overall rise in the NVMR reflects delayed marriage among the Chinese population and Korean women, but more persistent singlehood among lower-SES Korean men aged over 35. Notably, the faster growth of the NVMR among lower-SES groups has narrowed overall SES differences in marriage rates, eroding the historical pattern in which lower-SES individuals married earlier and more universally. In other words, marriage differentials based on SES are disappearing on absolute levels. This suggests that while financial constraints remain a key influence, broader structural and cultural shifts — such as evolving gender norms and rising opportunity costs — are also critical for understanding recent marriage declines in East Asia.