BACKGROUND: Vitamin D's role is noticeable on homeostasis of calcium and phosphorous and bone mineralization. Some studies prove that vitamin D has a role in reproductive pathways in male and females and its direct relationship with serum androgen levels in males. The common problem of infertility can be seen in 10%-15% of couples. 25%-50% of all infertilities is due to a male factor, and fertility disturbances are common in male CKD patients. OBJECTIVES: This study aimed to figure out the effect of serum vitamin D levels on semen analysis parameters and reproductive hormones before and after renal transplantation in ESRD patients. METHODS: This double-blind randomized clinical trial was carried out on 70 ESRD males (21-48 years old) who were candidates for renal transplantation at Sina hospital between 2021 and 2022. Participants were divided into two groups randomly. First group was supplemented by vitamin D (50,000 units weakly until 3 months), and no intervention was done in the second group. Vitamin D levels, LH, FSH, creatinine, glomerular filtration rate (GFR), calcium, total and free testosterone, PTH, sexual function, and semen analysis parameters were evaluated in a determined interval before and after (three and 6 months) kidney transplantation. RESULTS: Vitamin D levels were noticeably higher in case group in comparison to the control group ( CONCLUSION: Prescription of vitamin D as a supplementation doesn't improve sperm quality (sperm count, motility, morphology, and volume) and reproductive hormones (LH, FSH, free and total testosterone) after kidney transplantation in male CKD patients.