Lagerstroemia speciosa extracts and their active ingredient, corosolic acid exhibits significant anti-diabetic activity in humans. A reliable and reproducible high performance liquid chromatography (HPLC) and high performance thin layer chromatography (HPTLC) methods have been developed for the quantitative determination of corosolic acid in Lagerstroemia speciosa leaves and extracts. The methods developed have demonstrated good precision and recovery with % RSD less than 2%. The contents of corosolic acid determined by HPLC and HPTLC methods are in good agreement. The methods developed have also been employed for quantitative determination of corosolic acid in Lagerstroemia speciosa leaves and extracts. HPLC method has been found suitable for the quantitative determination of corosolic acid in dosage forms also.