Transtubular potassium gradient (TTKG) reflects the function of potassium secretion of kidney by the cortical collecting duct. However, association of tubular potassium secretory function and clinical outcomes in chronic renal disease has not been established. Therefore, we investigated the relationship between TTKG and chronic kidney disease (CKD) progression. Data were retrieved from the KoreaN Cohort Study for Outcome in Patients With Chronic Kidney Disease (KNOW-CKD) cohort. Among 2,238 participants, a total of 1,770 patients were included in this analysis after excluding patients without follow up data (n=59) or with missing data for baseline urinary osmolality and electrolyte level (n=189), urinary sodium < 25mEq/L (n=66), and urine osmolality < serum osmolality (n=154). The study endpoint was CKD progression, defined as a composite of more than 50% decrease in eGFR from baseline values, or end stage renal disease. During a median follow-up of 3.5 years (6,264 person-year), 460 participants reached the renal endpoint. CKD progression events occurred in 219 (37.1%), 163 (27.6%), and 78 (13.2%) patients in the lowest, middle, and highest TTKG tertile groups, respectively. In cause-specific competing risk analysis, the highest tertile was associated with significantly lower risk of adverse renal outcome compared to the lowest tertile (HR, 0.70; 95% CI, 0.53-0.92; P=0.010). When TTKG was treated as a continuous variable, 1 increase in TTKG was associated with a 6% lower risk of CKD progression (HR, 0.94; 95% CI, 0.89-0.99; P=0.011). This association was consistent across subgroups by age, sex, eGFR, proteinuria, and BMI. This study shows that higher TTKG is associated with a significantly lower risk of CKD progression, suggesting that it may be used as a predictor of adverse kidney outcome.