The protective effect of Biebersteinia Multifida on diazinon-induced toxicity in male Wistar rats was investigated over 8 weeks. Impacts of diazinon (10 mg/kg daily), Biebersteinia Multifida (500 mg/kg daily), and coadministration of them on oxidative stress parameters besides hematological and biochemical indices were assessed in various groups. The gas chromatography-mass spectrometry analysis was performed to identify the antioxidant components of plant extract by comparing the mass spectra and retention indices with those given in the literature. Pseudocholinesterase level demonstrated a significant attenuation in the Biebersteinia Multifida+diazinon-treated group in comparison to the diazinon group at the end of the 8th week. Statistical significant differences in hematological and biochemical indices were detectable when the diazinon group was compared to Biebersteinia Multifida+diazinon-treated rats. While diazinon destroyed hepatic and renal functions, Biebersteinia Multifida protected the liver and kidney from diazinon toxic effects by normalizing related function indices at the end of the 8th week. By diminishing malondialdehyde and enhancing the ferric-reducing power, Biebersteinia Multifida minimized the hazardous effect of diazinon-induced oxidative stress. Following these results, the beneficial effects of Biebersteinia Multifida in reducing the toxicity of diazinon should be taken into consideration.