The impact of the coronavirus disease 2019 (COVID-19) vaccination on humoral and cellular immunity in transplant recipients remains unknown. We report the case of a 78-year-old kidney transplant recipient who experienced acute T cell-mediated rejection after receiving the second dose of the BNT162b2 mRNA COVID-19 vaccine (Pfizer-BioNTech). She had no history of acute rejection throughout the 13 years after deceased donor kidney transplantation. Fifteen days after receiving the second dose of the BNT162b2 vaccine, the recipient visited our center with a mild headache and fever. Her serum creatinine level had increased from 0.61 to 4.95 mg/dL. Kidney allograft biopsy indicated acute T cell-mediated rejection (grade IB) with no pathologic evidence of antibody-mediated rejection. Anti-severe acute respiratory syndrome coronavirus 2 spike-immunoglobulin G and -immunoglobulin M measurements were weak positive and negative, respectively. Careful monitoring of kidney allograft function is vital for transplant recipients undergoing COVID-19 vaccination.