With the recently increased understanding of the roles of B cells in immune response and autoimmune pathogenesis, various techniques have been used for the detection of IL-10 production in B cells. In this chapter, we describe several commonly used methods for the effective detection of IL-10 in B cells at both mRNA and protein levels, including quantitative PCR analysis, intracellular staining of IL-10 by flow cytometry, ELISA assay for secreted IL-10 detection, and ELISPOT assay of enumerating IL-10-producing B cells. Moreover, we provide a detailed protocol for the detection of IL-10-producing B cells in situ by immunofluorescence microscopy. Together, the application of these described methods for the detection of IL-10 will facilitate the characterization of B cell subsets with regulatory functions and enhance our current understanding on the critical roles of B cells in immune response and autoimmune development.