A simple, accurate liquid chromatography with tandem mass spectrometry (LC/MS-MS) method has been developed and validated in human plasma. The method employed liquid-liquid extraction. Samples containing Irbesartan were chromatographed on a Hypersil gold column (C18, 5μm, 100 x 4.6 mm) at a temperature of 40°C. The isocratic mobile phase composition was a mixture of 2 mM ammonium formate (pH 4.0) / methanol (20:80 v/v), which was pumped at a flow rate of 0.5 mL / min with split ratio of 20:80.The retention time under these chromatographic conditions was found to be 2.20 minutes with run time 2.82 minute. Ethyl acetate & n-Hexane (80:20, v/v) was found to be good extracting and produced a satisfactory chromatogram. The developed LC/MS-MS method was found to be selective, simple, sensitive, accurate and linear for the analysis of Irbesartan in human plasma. The retention time and inturn run time was very short, hence required less mobile phase for the method, making it more economical and rapid. The method was applicable for the pharmacokinetic study of Irbesartan