A simple, selective, and sensitive liquid chromatographic method has been developed and validated for quantitative determination of Imatinib mesylate in rat serum. Efficient chromatographic separation has been performed on a Zorbax Extend (5 microm, 4.6 x 250 mm) double end-capped C(18) column using a mobile phase consisting of methanol and aqueous triethyl amine (pH 10.5; 1%, v/v) (60:40, v/v) in an isocratic mode at a flow rate of 1 mL/min. Simple and effective liquid-liquid extraction technique has resulted in consistent and high recoveries (90.32-95.86%) at all concentrations studied. The method has demonstrated linearity from 25 to 1600 ng/mL with a regression coefficient of 0.9995. Accuracy of the method is acceptable with intra-batch %bias between -2.34 to 3.42 and inter-batch %bias between -2.17 to 3.45. The method has demonstrated high sensitivity with lower limit of quantification of 25 ng/mL and excellent stability of Imatinib mesylate in serum. The method is found to be rapid, reliable, and suitable for in vivo pharmacokinetic study.