Background:Paraquat which is used as herbicide, decreases reduced glutathione(GSH) and increases oxidized glutathione (GSSG) via oxidative stresspathway and formation of ROS (Reactive Oxygen Species). Highperformance liquid chromatography (HPLC) with fluorescencedetector is one of the best methods for assessment of glutathione insamples like plasma which contains low level of this substance forevaluation of many of diseases. The purpose of this study was toevaluate the changes of glutathione quantity due to effect of paraquatin rat plasma with the use of HPLC.Methods:In this study the fluorescence substance 9-fluorenylmethylchloroformate(FMOC) was used for derivatization of amine group ofglutathione. To do this, the rat obtained plasma, which had beenexposed with four doses of paraquat (20, 30, 40, and 60 mg/kg), wasmixed with acetonitryl and centrifuged at 5000 rpm for proteinprecipitation. The supernatant was completely dehydrated in a 40oCwater bath under air flow with an air pump. 506l tap water, 50 6lborate buffer 0.5M, pH=9 and 100 6l FMOC 500 6g/ml were addedand then was left at room temperature for 15 min for completion ofderivatization. After that, 206l of this solution was injected into aHPLC with C18 column, mobile phase methanol: phosphate buffer(60:40 v/v) and ex=260nm, em=315 nm.Findings:According to the obtained results, the amount of oxidized glutathionewas increased significantly only in the dose of 60 mg/kg incomparison with the control group (p