INTRODUCTION AND HYPOTHESIS: Nocturia affects health and quality of life (QoL). Current medical treatments can cause severe adverse effects, especially when treating elderly patients. Endogenous melatonin has a physiologic role in urinary bladder function, and the exogenous one may be beneficial for this condition. This article aims to evaluate the effectiveness and safety of melatonin for ameliorating nocturia in older women. METHODS: This randomized, double-blind, placebo-controlled trial was conducted at a university hospital in Thailand. Sixty women with nocturia, aged > 55 years, were prospectively recruited and were later randomly allocated to treatment (melatonin 2 mg/day, n = 30) and control (placebo, n = 30) arms for 2 weeks. Outcome measures included nocturia episodes, nocturia-related parameters, Nocturia Quality of Life Questionnaire (N-QoL) scores, and adverse events. RESULTS: The treatment and control groups were comparable in mean age (65.9 + 7.5 vs. 68.5 + 6.3 years). Both groups had comparable causes of nocturia with a baseline median voiding frequency of 2.3 (1.3, 6.3) and 2.3 (1.7, 5.3) episodes/night, respectively. The treatment group had significantly better outcomes than the placebo group in terms of median reduction in nocturia [-1.0 (-3.0, 0.0) vs. 0.0 (-2.3, 1.3) episodes/night; p < 0.001], increased median duration of the first uninterrupted sleep [1.0 (-0.3, 4.5) vs. 0.0 (-3.0, 2.3) h; p < 0.001], and improvement in N-QoL scoring, especially in the sleep/energy subscale (p = 0.019) and the total score (p = 0.016). Adverse events were comparable between groups. CONCLUSIONS: Melatonin can be considered a safe and effective treatment for nocturia in elderly women.