The development of acute rejection can only be considered in cases with increasing serum creatinine in patients with kidney transplantation. However, the serum creatinine itself is not specific but also accurate for detection of acute rejection. So The specific biomarker is required for acute rejection of kidney transplant. In this study, the investigators will enroll 200 consecutive kidney transplant patients in Seoul National University Hospital and follow up. Serial collection of urine and serum will be done. Acute rejection specific urine metabolite will be found by LC MS/MS.

Inclusion Criteria:

• Kidney transplant patients in Seoul National University Hospital
• Patients with triple maintenance immunosuppression including Tacrolimus, mycophenolate and steroid

Exclusion Criteria:

• History of other organ transplantation
• ABOi and/or crossmatch(+) transplantation

Study population includes low or moderate risk kidney transplantation. They should have triple immunosuppression.