Background. Urinary incontinence is one a lower urinary tract disorder prevalent in women of reproductive age. The role of vitamin D in urinary incontinence has not been proven, despite extensive study.Objectives. This study aimed to investigate the relationship between serum 25(OH)D levels with urinary incontinence in Iranian reproductive-aged women. Material and methods. This cross-sectional study was conducted on 437 samples of women aged 15-49 years who complained about any urinary tract disease and were referred to two comprehensive health centres in Izeh, Iran, from May to September 2017. Serum 25(OH)D was assessed using High-Performance Liquid Chromatography after 8-12 hours of fasting. The severity of urinary incontinence was measured using the International Consultation on Incontinence Questionnaire-Short Form (ICIQ-UISF) and was confirmed by a gynaecologist. Results. The serum levels of 25(OH)D in UI patients were significantly lower than the comparative group (p < 0.05). The association between vitamin D levels and UI subgroups was significantly positive (p = 0.001). Vitamin D also had a negative coefficient of correlation (-0.096) with the severity of urinary incontinence (p = 0.001). Conclusions. There was a significant relationship between serum 25(OH)D levels and the severity of urinary incontinence among Iranian reproductive-aged women. A low serum 25(OH)D level is also significantly related to UI subgroups.