The organic components such as chlorophyll, carotenoids, ascorbic acid, proteins and sugar of healthy and infected mango (Mangifera indica L.) leaves were analyzed. All the organic components in mango leaves were affected greatly due to infection with Alternaria alternata (Fr.) Keissl. Chlorophyll, carotenoids, ascorbic acid, proteins and sugar were found to be decreased in the infected mango leaves by 20.27%, 14.06%, 32.86%, 31.73% and 18.02% respectively. Ascorbic acid and proteins contents were found to be highly affected.