The progression patterns of chronic kidney disease (CKD) vary globally. However, ethnic differences in CKD progression remain understudied, particularly between Asian and Western population. Therefore, we aimed to investigate ethnic disparities in CKD progression by comparing two nationwide cohorts from South Korea (KNOW-CKD) and the United States (CRIC). A total of 4,953 participants were recruited. The primary outcome was CKD progression, defined as a halving of estimated glomerular filtration rate (eGFR) or kidney failure with renal replacement therapy. We compared this outcome between two cohorts and among Asians, Whites, and Blacks using cause-specific competing risk model. In the secondary outcome analysis, we further compared eGFR decline rates and all-cause mortality. Of the 4,953 participants included (median age: 59 years; 42.9% female), CKD progression occurred in 1,283 and 570 in the KNOW-CKD and CRIC cohorts, with incidence rates of 67.9 and 41.7 per 1,000 person-years, respectively. The hazard ratio for the KNOW-CKD vs. CRIC was 1.71 (95% confidence interval [CI], 1.50–1.95). Additionally, the annual eGFR decline was steeper in KNOW-CKD participants than in CRIC participants (-2.51 vs. -1.14 ml/min/1.73m²). Notably, Asians from the CRIC cohort exhibited a similar eGFR slope to those from KNOW-CKD (-2.10 ml/min/1.73 m2), while the slope was -1.47, and -0.81 ml/min/1.73m² for Blacks and Whites, respectively. In contrast, the risk of mortality was significantly lower in KNOW-CKD participants compared with CRIC participants (HR, 0.53; 95% CI, 0.40–0.71). CKD progression was faster in Korean cohort compared to US cohort, with Asians in both cohorts showing similar eGFR decline rates. However, Korean cohort had a significantly lower risk of mortality, indicating potential ethnic or regional differences in disease progression and survival.