Background: The diagnosis of a failing renal allograft is a complex process. Radionuclide imaging is a great method that gives additional details about the perfusion and function of the transplant without harming the allograft to avoid invasive renal biopsy and its complications. Objective: The aim of the current study is the differentiation between acute renal graft rejection and acute tubular necrosis in the early post-transplant period using dynamic 99mTc-DTPA scintigraphy. Patients and methods: A retrospective study was conducted and included 56 cases suffering from acute deteriorated graft function in first year after renal transplantation. We reviewed their dynamic 99mTc-DTPA images findings which performed at time of graft dysfunction and compared with graft biopsy results as a gold standard. Results: Acute renal rejection was diagnosed in 16 cases; acute tubular necrosis was evident in 28 cases and 12 cases suffering from both elements. By analysis, the mean ages of cases of acute renal graft rejection were 29.3 (SD 9.4) years, cases of acute tubular necrosis were 30.1 (SD 8.1) years, and cases of both elements were 30.7 (SD 5.6) years old. The scintigraphic results showed perfusion and delayed tracer excretion were the most significant predictors (P-value =0.001). The sensitivity and specificity of renal scintigraphy for the detection of acute tubular necrosis (ATN) were 89.3% and 96.4%, respectively; in acute rejection (AR), were 97% and 99%. Conclusion: A non-invasive procedure with high sensitivity and specificity to distinguish between acute renal rejection and acute tubular necrosis is dynamic renal scintigraphy using 99mTc-DTPA.