Background <p>Abnormal circadian pattern of urinary sodium excretion was associated with high blood pressure and target-organ injury. However, whether urinary circadian pattern of sodium excretion is associated with chronic kidney disease (CKD) progression has not been elucidated.</p> Methods <p>We evaluated 1604 participants with CKD in this retrospective cohort study. We studied the association between clinical outcomes and day: night ratio of urinary sodium excretion, using urine collected separately during daytime and nighttime. The primary outcome was defined as a decrease of ≥ 30% in eGFR from baseline or initiation of renal-replacement therapy. The secondary outcome was a decrease of ≥ 50% in eGFR from baseline or initiation of renal-replacement therapy.</p> Results <p>The primary and secondary outcome occurred in 319 and 247 patients during 5710.2 person-years of follow-up, respectively. The Kaplan-Meier (KM) analysis showed an association between lower day: night ratio of urinary sodium excretion and primary and secondary outcome (both <i>P</i> &lt; 0.05). In multivariate analysis, fully adjusted hazard ratios (95% confidence intervals) for patients with day: night ratio of urinary sodium excretion in the lowest quartile were 2.29 (1.55–3.39) for the primary outcome and 2.42 (1.53–3.85) for the secondary outcome, compared to the highest quartile.</p> Conclusion <p>Abnormal circadian pattern of urinary sodium excretion, characterized by a lower day: night ratio of urinary sodium excretion, is associated with CKD progression in CKD patients. These findings suggest day: night ratio of urinary sodium excretion may serve as a marker to recognize CKD progression.</p> Clinical trial number <p>Not applicable.</p>