Alternaria leaf spot or black leaf spot caused by Alternaria brassicicola is the devastating diseases of mustard-rapeseed in Bangladesh, and can cause yield loss up to 60% every year. A total of 27 cultivars of Brassica spp. where Brassica rapa (13), B. juncea (5) and B. napus (9) were selected for resistance screening against A. brassicicola. Two inoculation methods viz. detached leaf and seedling inoculation were assessed for checking the validation of inoculation technique using cultivated mustard-rapeseed varieties in Bangladesh a method to measure resistance to A. brassicicola. A significant positive correlation between the results of two inoculation methods was found in this study. The detached leaf technique was more suitable due to development of clear symptoms on the leaves within 36 hrs, and suitable for screening large scale genotypes for resistance. The 3rd leaves of 30 day-old were more suitable for inoculation having severe symptoms than the 4th leaves. Among 27 Bangladeshi mustard-rapeseed cultivars all cultivars expressed susceptible reaction to A. brassicicola, except BINA Sharisha-8, as it had border line resistance.