A colorimetric method for the determination of tetracycline and oxytetracycline is developed. It depends on nitration and reaction of the nitroderivatives with acetone in the presence of potassium hydroxide. A highly colored complex is produced. Variables such as temperature) time of heating, volume of nitrating mixture, acetone and potassium hydroxide have been evaluated to permit the selection of the most advantageous technique. Beer's Law is obeyed over the concentration range from 0.004 – 0.04 mg ml for tetracycline and oxytetracycline.