Ischemia-reperfusion injury is the major cause of organ dysfunction or even nonfunction following transplantation. It can attenuate the long-term survival of transplanted organs. To evaluate the severity of renal ischemia injury determined by histology, we applied laser- (442 nm and 532 nm) induced fluorescence (LIF), mitochondria respiration, and membrane swelling to evaluate 28 Wistar rats that underwent left kidney warm ischemia for 20, 40, 60, or 80 minutes. LIF performed before ischemia (control) was repeated at 20, 40, 60, and 80 minutes thereafter. We harvested left kidney tissue samples immediately after LIF determination for histology and mitochondrial analyses: state 3 and 4 respiration, respiration control rate (RCR), and membrane swelling. The association of optic spectroscopy with histological damage showed: LIF, 442 nm (r2 = 0.39, P < .001) and 532 nm, (r2 = 0.18, P = .003); reflecting laser/fluorescence-induced, 442 nm (r2 = 0.20, P = .002) and 532 nm (r2 = 0.004, P = .67). The associations between mitochondria function and tissue damage were: state 3 respiration (r2 = 0.43, P = .0004), state 4 respiration (r2 = 0.03, P = 0.38), RCR (r2 = 0.28, P = .007), and membrane swelling (r2 = 0.02, P = .43). The intensity of fluorescence emitted by tissue excited by laser, especially at a wave length of 442 nm, was determined in real time. Mitochondrial state 3 respiration and respiratory control ratio also exhibited good correlations with the grade of ischemic tissue damage.