Blackleg caused by Leptosphaeria maculans (Desm.) Ces. & De Not. is one of the most serious diseases in canola production. A high level of blackleg resistance has been shown in Brassica carinata A. Braun (BBCC) and new synthetic hexaploid Brassica species (AABBCC) developed from the crosses of B. rapa L. and B. carinata. Blackleg resistance from B. carinata and hexaploid Brassica accessions was transferred into B. napus L. using interspecific hybridization followed by backcrossing to a susceptible B. napus cultivar ‘Westar’ three or four times and selfing one or two times to produce pure lines. Leptosphaeria maculans isolate 03-15-03 was used to select the resistant plants in each generation using cotyledon inoculation, and four L. maculans isolates (03-15-03, 3-42-6, 09stonewall9553, and PG4-1-M) were utilized in advanced generations. In the cross of B. napus ‘Westar’ and B. carinata, all plants in the F1 showed a high level of resistance to L. maculans isolate 03-15-03. According to the chi-square testing for goodness of fit, the segregation of resistant and susceptible plants fit a 1:1 ratio in the BC1, BC3, and BC4. In the BC3F2, two families followed a 3:1 segregation ratio of resistant and susceptible plants. The results suggest that the resistance to L. maculans transferred from B. carinata into canola ‘Westar’ was controlled by a single locus. Embryo rescue tissue culture was used to obtain F1 plants of the crosses of ‘Westar’ and synthetic hexaploid Brassica accessions. In the BC1 and BC2, most families did not fit a 1:1 segregation ratio of resistant and susceptible plants. The segregation of resistant and susceptible plants fit a 3:1 ratio when inoculated with L. maculans isolates in the BC1F2-3.1.1s and BC1F3-3.1.1.1ss families. Meanwhile, the BC2-3.1.1 family also followed a 1:1 segregation of resistant and susceptible plants inoculated with L. maculans isolate 03-15-03. The results suggest that the resistance to L. maculans introgressed from synthetic hexaploid Brassica species into B. napus is most likely controlled by a single locus. / May 2016