During the investigation on the isolation of aureomycin from fermentation broth, it was observed that the stability of aureomycin depended upon the pH and temperature of the solution. The present report deals with the influence of pH and temperature on the stability of the antibiotic. The destruction of aureomycin in acid solution was followed by measuring colorimetrically anhydroaureomycin formed during the experimental period. The optical density of the developed color in dilute hydrochloric acid is proportional to the concentration of aureomycin. The concentration of anhydroaureomycin is also proportional to the optical density of the color.