Blackgram is a short duration legume crop affected by fungi, bacteria, viruses and nematode. Among the fungal diseases, Alternaria leaf spot disease caused by the Alternaria alternata (Fr.) Keissl. is becoming a major problem in blackgram fields of Andhra Pradesh. The survey conducted during rabi 2017-18 revealed that Alternaria leaf spot disease severity was more or less same in both the mandals surveyed. The disease kept on increasing with increase in the age of the crop. The disease progressed from 6.49% at 40 DAS to 17.89% at 50 DAS and further to 50.62% at 60 DAS in Ponnur mandal. In Amruthuluru mandal, the disease progress was 5.49% at 40 DAS to 19.16% at 50 DAS and 51.29% at 60 DAS. The pathogen isolated from the leaf spot symptom was identified as A. alternata by comparing with standard descriptions made by previous reports based on characteristics of the colony, hyphae, conidiophore and conidia.