A simple, selective and accurate high performance liquid chromatographic (HPLC) method was developed and validated for the analysis of esomeprazole magnesium trihydrate (ES) in tablets. Chromatographic separation was achieved isocratically on a C 18 column utilizing a mobile phase of acetonitrile/phosphate buffer (60:40, v/v, pH 7) at a flow rate of 1.0 mL/min with UV detection at 205 nm. Lansoprazole was used as an internal standard (IS). The calibration curve of ES was linear in the range of 100 similar to 1000 ng/mL (r = 0.9992, n = 4). The RSD values for intra- and inter-day precision were 0.66 similar to 0.86% and 0.84 similar to 1.11%, respectively. The proposed method was successfully applied to the determination of ES in tablets. The mean recovery for ES from the tablets ranged between 97.82 similar to 98.22%. ES was subjected to neutral, acid and alkali hydrolysis as well as oxidation, dry heat treatment and photodegradation. Being simple, accurate and selective, the method can be used for routine quality control analysis.