MicroRNAs(miRNAs) are a class of small non-coding RNAs that regulate gene expression at post-transcriptional level. They play important roles in multiple physiological and pathological processes, including development, cell proliferation，apoptosis，metabolism and tumorigenesis, etc. Mouse B cell at different development stages were isolated by FACS and analyzed the miRNAs profile using TaqMan® Low Density Array. The data showed that 9 miRNAs were significantly up-regulated in the pre-B cells. Functional clustering and pathway analysis of 1102 predicted target genes of these miRNAs showed that about 4% of the genes involved in immune system processes, including Bcl2, Kit, etc. A dual luciferase reporter system and Western blot were used to validate the interaction between foxO1 and miR-19b, miR-142-3p, miR-106b, miR-182, miR-133b. The results show that miR-133b can directly regulate the expression of foxO1. According to the foxO1 expression profile of human and mouse, the expression pattern is negatively correlated with that of miR-133b, indicating that miR-133b may be involved in the regulation of foxO1 in B cell development.