The stem bark of Acacia nilotica is used as a powerful astringent and the decoction is used as gargle for throat troubles and stomatitis.q3 Bark contains several polyphenols such as catechin,epicatechin, dicatechin, quercetin and tannin. Gallic acid has been reported to have antidiabetic,antithrombotic, anti inflammatory and anticarcinogenic activities. A simple, precise and accuratehigh-performance thin layer chromatographic method has been established for the determination of Gallic acid in the bark powder of Acacia nilotica Linn. The acetone extract of the bark powder wasused for the experimental work. Separation was performed on Silica gel 60 F254 HPTLC plates with Toluene: Ethyl acetate: Formic acid (6:4:0.8 v/v), as mobile phase. The plate was scanned in the densitometric absorbance mode at 280 nm. Gallic acid response was linear over the range 2-7 μg ml-1. The HPTLC method was validated in terms of sensitivity, accuracy, precision and reproducibility. The concentration of gallic acid in the bark powder was found to be 0.86%.