A Kinetic method is based on the degradation rate of tetracycline (TC) or oxytetracycline (OTC) to their anhydro derivatives with subsequent spectrophotometric measurements. With optimized degradation rate parameters, calibration curves relating decrease in absorbance difference (of alkaline solution versus acid solution) as a funotion of concentration in a range of 0.8-4.0 mg% are linear with negligible interecept. The method is applicable for powder and capsule assays and gives results within the pharmacopoeial limits.