The Arabidopsis AtmiR156b gene was expressed in Brassica napus under the control of the cauliflower mosaic virus (CaMV) 35S promoter and the seed-specific napin promoter. Seed carotenoid levels, branching habit, seed yield, and seed weight were examined in the transgenic B. napus. Our results demonstrated that constitutive expression of AtmiR156b in B. napus resulted in enhanced levels of seed lutein and β-carotene and a 2-fold increase in the number of flowering shoots, whereas AtmiR156b driven by the napin promoter did not affect these traits. This suggested that enhancement of seed quality and shoot branching are both related to AtmiR156b expression patterns. Seed yield and seed weight varied significantly within the transgenic lines. However, one line was found to have enhanced seed carotenoid levels but unchanged seed weight or yield. These data suggest that AtmiR156b gene expression could be applied in plant breeding initiatives for enhancing carotenoid production in canola and other crop species.