A densitometric HPTLC method has been established for simultaneous quantification of sennosides A and B and gallic acid in a laxative polyherbal pharmaceutical dosage form. Aluminum plates coated with silica gel 60 F254 as stationary phase were used with toluene-ethyl acetate-formic acid-methanol 8:8:4:5 (v/v) as mobile phase. Densitometric analysis was performed at 270 nm. Amounts of sennosides A and B and gallic acid were 10.48, 9.03, and 2.96% (w/w) respectively. The method was validated for specificity, linearity, precision, repeatability, and accuracy. Calibration plots were linear in the concentration range 114.0–427.5 ng per band for sennosides A and B and 100–375 ng per band for gallic acid. The correlation coefficients were 0.995, 0.998, and 0.997 for sennosides A and B and gallic acid, respectively. Relative standard deviation (RSD, [%]) for instrumental precision and repeatability of the method was 0.74, 0.49, 0.43 and 1.11, 1.08, 0.89 for sennosides A and B and gallic acid, respectively. Recovery was 96.28–97.22% for sennoside A, 98.06–100.84% for sennoside B, and 97.09–98.07% for gallic acid. The method is simple, precise, specific, accurate, and economical. It can be used for routine analysis of formulations containing Senna (Cassia angustifolia) and Haritaki (Terminalia chebula) extracts.