MicroRNAs (miRNAs) have important roles in regulating stress-response genes in plants. However, identification of miRNAs and the corresponding target genes that are induced in response to cadmium (Cd) stress in Brassica napus remains to be explored. In the current study, we sequenced three small-RNA libraries from B. napus after 0, 1, and 3 days of Cd treatment. This identified 44 known miRNAs (belonging to 27 families) and 103 novel miRNAs. A comprehensive analysis of miRNA expression profiles found 39 differentially expressed miRNAs in control and Cd-treated plants; 13 differentially expressed miRNAs were confirmed by qRT-PCR. Characterization of the corresponding target genes indicated functions in processes that include transcription factor regulation, biotic stress response, ion homeostasis, and secondary metabolism. Furthermore, we propose a hypothetical model of the Cd-response mechanism in B. napus. Combined, our data suggest that miRNAs have essential roles in the response to Cd stress in B. napus.