The lipase inhibitory activities of four main components from the rhizomes of Alisma orientale (Sam.) Juz. were evaluated by an in situ high-performance thin-layer chromatography (HPTLC)‒bioautographic assay taking orlistat as control standard. The order of relative activity was alisol B 23-acetate > alisol B > alisol A > alisol C 23-acetate. With that, an accurate, efficient and sustainable HPTLC method was developed to simultaneously determine the four lipase inhibitors from the methanolic extracts of Alismatis Rhizoma (AR). The method was carried out on HPTLC glassed plates (20 × 10 cm) coated with silica gel 60 F254 (0.2 mm thickness) using a mixture of cyclohexane and ethyl acetate (1:1, V/V) as the mobile phase. The RF values found for alisol B 23-acetate, alisol C 23-acetate, alisol B and alisol A were 0.62, 0.42, 0.28 and 0.09, respectively. The method was validated for specificity, linear range, precision, stability, and recovery. The results determined by scanning densitometry showed no significant difference to the results obtained by HPLC. The developed method was verified to be trustworthy for the evaluation of quality markers in AR.