The data for vitamin D (VD) pleiotropy is rapidly accumulating. A typical pleiotropic effect of VD is proteinuria (PU) reduction The aim of our study is to assess the antiproteinuric properties of cholecalciferol supplementation in Bulgarian kidney transplant recipients (KTRs). The study encompassed KTRs who paid regular visits between 1.11.2016 and 31.12.2016 in our center. Standard blood and urine tests were performed, including 24-h urine specimen for PU and serum 25-hydroxyvitamin D (25VD) level. VD insufficient KTRs (25VD < 75 nmol/L) were given oral cholecalciferol. Supplementation daily dose varied according to the initial VD status: 25VD < 50 nmol/L 4000 IU, between 50 nmol/L and 75 nmol/L 2000 IU. KTRs with unstable kidney function, rejection, hypercalcemia/hyperphosphatemia and change in immunosuppressive treatment were excluded. Control studies were performed between 1.05.2017 and 30.06.2017, evaluating 25VD and PU. Assessment was performed in the overall group and according to the posttreatment 25VD. Statistical anal. included descriptive anal., Wilcoxon signed-rank test, Fisher's exact test (SPSS 22.0), level of significance adopted was p < 0.05. Screening for outliers was performed by using the Z-score method. Total 25VD was measured by a validated LC-MS/MS method. Fifty-four KTRs met the inclusion criteria. In the overall population, supplementation improved significantly VD status (VD level 40.50±16.30 nmol/L prior to vs 68.51±23.26 nmol/L after treatment, p < 0.001), without significant reduction in PU (from 0.31 ±.33 g before to 0.29 ± 0.34 g after supplementation, p = 0.404). However, a significant reduction in proteinuria was detected in post-treatment 25VD > 75 nmol/L (from 0.35 ± 0.42 g to 0.23 ± 0.29 g, p = 0.005). We demonstrate proteinuria reduction in KTRs after cholecalciferol supplementation above the post-treatment value of 75 nmol/L 25VD, indicating that this may be a possible supplementation target level. Further studies are needed to clarify the link between cholecalciferol supplementation and proteinuria after kidney transplantation.