A case of acute kidney injury (AKI) strongly suspected to be drug-induced (oxaliplatin and non-steroidal anti-inflammatory drug) is discussed regarding the mechanism of a reduced glomerular filtration rate responsible for the development of AKI. Urinary biochemical tests are useful for the differential diagnosis of pre- renal (functional) AKI and intrinsic (structural) AKI(so-called acute tubular necrosis). In this case, although a comprehensive differential diagnosis using these parameters supported intrinsic AKI, only one pa- rameter, fractional excretion of urea (FEurea), indicated the existence of prerenal AKI. As a result of treatment with the appropriate management of body fluid in addition to avoiding nephrotoxic medications, AKI rapidly improved. FEurea revealed the underlying mechanism of AKI. [Review].