A colorimetric method for the quantitative determination of diclofenac sodium and mefenamic acid in pure form and in pharmaceutical preparations was developed. It was based on the inter-action of the secondary aromatic amine with p-dimethyl-aminocinnamaldhyde in acidified absolute methanol medium to form very stable red [λmaxat 538 nm in case of diclofenac sodium] or blue [λmaxat 665 nm in case of mefenamic acid] products. Beer's law was obeyed over the ranges 10–80 μg ml−1and 1–8 μg ml−1for diclofenac sodium and mefenamic acid, respectively. The reactants were heated on a boiling water bath for 6 and 5 mins for each drug, respectively. Optimization of the different experimental conditions were studied. The mean percentage recoveries were found to be 100.73 ± 0.87% & 100.73 ± 0.44%, respectively. The method was applied successfully for the determination of some pharmaceutical formulations.