A high performance thin layer chromatographic (HPTLC) method was developed and validated for simultaneous determination of rhein and aloe-emodin, major anthraquinone constituents, in S. alata leaves. The separation was performed on a silica gel 60 F₂₅₄ HPTLC plate using ethyl acetate: methanol: water (100:17:10, v/v/v) as the development system. Validation of the analytical method for rhein and aloe-emodin promoted acceptable parameters. Good linearity in the range of 40-480 ng/band was obtained while intra-day and inter-day precisions were shown to be precise with relative standard deviations of less than 5%. The average percentage recoveries of rhein and aloe-emodin were 98.8% and 98.9%, suggesting acceptable accuracy. The content of rhein and aloe-emodin in S. alata leaves collected from 5 different provinces in Thailand analyzed by the validated HPTLC method were in the ranges of 0.098 ± 0.017 - 0.30±0.02%, w/w, and 0.081 ± 0.0006 - 0.34 ? 0.0009 %, w/w, respectively. Five commercial products of S. alata tea available in the market were purchased and analyzed for rhein and aloe-emodin contents. The contents of rhein and aloe-emodin in the tea samples were in the ranges of 0.085 ± 0.004 - 0:23 ± 0.04%, w/w, and 0.096 ±0.006 - 0.30 ± 0.01 %, w/w, respectively. The HPTLC method is rapid, reliable, sensitive and economical for routine analysis of rhein and aloe-emodin contents in-S. alata leaf raw materials and its commercial products.