Potato early blight is one of serious diseases on potato plants in Egypt. This disease caused by Alternaria solani which could be very sever on the vegetative growth of the plants. It also infect the tubers and reduce their quality. In this research work, some chemicals and compost were tested on disease incidence and mycelial growth of the causal organism. The fungicides fenarimol 1.2% (Rubigan) and deconazole 10% (Topas) were more effective than the other chemicals and compost extract. In greenhouse experiments, results indicated that the most effective treatments were fungicides, compost extract followed by chemicals. Considerable increases in activity of the oxidative reductive enzymes (peroxidase and polyphenoloxidase) as well as chitinase enzyme were recorded in plants grown from treated potato tubers. In field experiments results indicated that the most effective treatments were the fungicides, compost extract and chemicals compared to the unntreated control. It could be suggested that a compost extract and chemicals i.e. Bion,salicylic acid,oxalic acid,Rubigan 12% and Topas could be used for controlling early blight of potato plants under field conditions