Vitamin D deficiency, persistent hyperparathyroidism, and bone loss are common after kidney transplantation (KTx). However, limited evidence exists regarding the effects of cholecalciferol supplementation on parathyroid hormone (PTH) and bone loss after KTx. In this prespecified secondary endpoint analysis of a randomized controlled trial, we evaluated changes in PTH, bone metabolic markers, and bone mineral density (BMD). At 1 month post-transplant, we randomized 193 patients to an 11-month intervention with cholecalciferol (4000 IU/d) or placebo. The median baseline 25-hydroxyvitamin D (25[OH]D) level was 10 ng/mL and 44% of participants had osteopenia or osteoporosis. At the end of the study, the median 25(OH)D level was increased to 40 ng/mL in the cholecalciferol group and substantially unchanged in the placebo group. Compared with placebo, cholecalciferol significantly reduced whole PTH concentrations (between-group difference of −15%;​ 95% confidence interval [CI] −25 to −3), with greater treatment effects in subgroups with lower 25(OH)D, lower serum calcium, or higher estimated glomerular filtration rate (p_int < 0.05). The percent change in lumbar spine (LS) BMD from before KTx to 12 months post-transplant was −0.2% (95% CI −1.4 to 0.9) in the cholecalciferol group and −1.9% (95% CI −3.0 to −0.8) in the placebo group, with a significant between-group difference (1.7%;​ 95% CI 0.1 to 3.3). The beneficial effect of cholecalciferol on LS BMD was prominent in patients with low bone mass p_int < 0.05). Changes in serum calcium, phosphate, bone metabolic markers, and BMD at the distal radius were not different between groups. In mediation analyses, change in whole PTH levels explained 39% of treatment effects on BMD change. In conclusion, 4000 IU/d cholecalciferol significantly reduced PTH levels and attenuated LS BMD loss after KTx. This regimen has the potential to eliminate vitamin D deficiency and provides beneficial effects on bone health even under glucocorticoid treatment.