Introduction: Prevalence of vitamin D deficiency among patients with kidney failure is about 70 to 80 percent. Among the main controversies in the field of patients with kidney failure is the relationship between vitamin D deficiency and prevalence and natural course of hypertension. Many studies have been conducted on the relationship between vitamin D levels and hypertension, but they have mostly been inconclusive and have generated inconsistent results. Materials and methods: This cross-sectional study was conducted on 120 patients with dialysis in three dialysis centers in Tehran, Iran. Vitamin D levels were measured by dialysis centers every three months for a year. Also, the centers recorded blood pressure after each dialysis session. These measurements were collected and their means for each patient were calculated and analyzed by backward multivariate linear regression in order to determine the association between blood pressure and levels of vitamin D. Besides, during the study, data on other confounding factors such as age, sex, weight, and so on were gathered. Levels of calcium, phosphorus, and PTH were also measured. A previously prepared checklist was used by the nurses in order to record patient data. Results: In this cross-sectional study, 101 dialysis patients were assessed, of which 45 were female and 56 were male. The mean age of the patients was 60 years. 55.6% of the patients had vitamin D deficiency (vitamin D <30 ng/ml). After entering and analyzing data, the serum level of vitamin D had a significant association with diastolic blood pressure, and Pearson correlation coefficient between diastolic blood pressure and serum levels of vitamin D was statistically significant (p<0.002). Conclusion: In this observational study, a significant linear association was found between serum levels of vitamin D and diastolic blood pressure in patients with dialysis. It seems that vitamin D levels had a negative association with diastolic blood pressure in those patients.