Alternaria blight caused by Alternaria brassicae and Alternaria brassicicola has become one of the important diseases of this crop in the country. Experiments were conducted at Genetics and Plant Breeding Research Farm of N. D. University of Agriculture and Technology, Kumarganj, Faizabad (U.P.) to evaluate fungicidal management of Alternaria blight .Three sprays of Nativo 75 WG @ 0.08%, one at DI, second and third at 15 days intervals and three sprays of Nativo 75 WG @ 0.08%, one at DI, second at flowering and third at poding stage showed low per cent disease severity, low infection rate, higher yield and higher avoidable yield loss compared to other treatments. These treatments are proved to be effective compared to other treatments. While control plot showed high per cent disease severity, high infection rate, lower yield and lower avoidable yield loss compared to other treatments. The maximum benefit : cost ratio (1:7.72) was obtained with two spray of Nativo 75 WG, one at FS and second at poding stage followed by three spray of Nativo 75 WG, one at DI, second and third at 15 days intervals (1:7.56). On the basis of above findings it may be concluded that Alternaria blight can causes extent of yield losses in yield of rapeseed-mustard up to 41.16% in eastern Uttar Pradesh. To manage the disease 3 sprays of Nativo @ 0.08 % was most economical and can be recommended to the farmers of blight prone areas.