A simple and precise reversed-phase high performance liquid chromatography (HPLC) method for the determination of gliclazide in human plasma was developed and validated. Using glipizide as an internal standard (IS), separation was achieved on Atlantis dC18 column. The mobile phase consisted of acetonitrile and water (pH= 2.5±0.2 adjusted with phosphoric acid) (55:45, v:v), and delivered at a flow rate of 1 ml/min. 0.5 ml plasma samples were deproteinized with dichloromethane and centrifuged. 100 µl supernatant clear solutions were injected to HPLC system. The eluent was monitored spectrophotometricly at 230 nm. No interference in blank plasma or of commonly used drugs was observed. The relationship between the concentration of gliclazide in plasma and peak height ratio of gliclazide to the IS was linear over the range of 0.05-10.0 μg/ml. Intra-day and inter-day coefficient of variation (CV) and bias were 3.1% to 6.8% and 3.8% to 9.3% respectively. Mean extraction recovery of gliclazide and the IS from plasma samples was 94% and 87% respectively. The method was applied to assess the stability of gliclazide under various conditions generally encountered in the clinical laboratory. Stability for processed and unprocessed samples was ≥ 90% and ≥ 93% respectively