Vonoprazan fumarate (vonoprazan) is a new kind of acid suppressant with potent acid inhibitory effects. Therefore, it has been administered to kidney transplant recipients for treatment or prophylaxis of steroid ulcers, refractory peptic ulcers, and gastroesophageal reflux disease. Because tacrolimus, which is a well-established immunosuppressant for kidney transplantation, and vonoprazan share the CYP3A4 system for metabolism, drug interactions are anticipated upon simultaneous administration. We retrospectively analyzed 52 kidney transplant recipients who were converted from rabeprazole, which has a small effect on the tacrolimus trough blood concentration ( C ₀), to vonoprazan between August 2016 and July 2019. We compared the tacrolimus C ₀/tacrolimus dose ( C ₀/ D ) before and after conversion and serum liver enzymes, serum total bilirubin, and the estimated glomerular filtration rate (eGFR). As a result, mean tacrolimus C ₀/ D before and after conversion was 1.98 ± 1.02 and 2.19 ± 1.15 (ng/mL)/(mg/d), respectively, ( p < 0.001). Additionally, mean aspartate transaminase (AST) before and after conversion was 18.6 ± 4.2 and 19.6 ± 5.2 IU/L, respectively, ( p = 0.037). Mean alanine transaminase (ALT) before and after conversion was 15.8 ± 5.5 and 17.6 ± 7.1 IU/L, respectively, ( p = 0.007). Mean eGFR before and after conversion was 50.6 ± 14.4 and 51.4 ± 14.7 mL/min/1.73 m², respectively ( p = 0.021). Mean AST, ALT, and eGFR were slightly but significantly elevated within normal ranges after conversion. In conclusion, our study suggests that the mean tacrolimus C ₀/ D was elevated significantly by converting from rabeprazole to vonoprazan, but it had little clinical significance. Vonoprazan can be administered safely to kidney transplant recipients receiving tacrolimus.