In vertebrates there are two acquired immune systems, i.e., humoral immune response and cellular immune response. Of mature cells (plasma cells), B cells are differentiated from early progenitor cells and are responsible for humoral immune response, which is an antigen-specific immune system producing antibodies. Normal development and differentiation of B cells require various specific transcription factors. Recently, we systematically analyzed the roles of some transcription factors at immature stage of B cell development using gene-targeting techniques in chicken immature B cell line, DT40 cells, which are very advantageous for analyzing the physiological functions of the B cell-specific transcription factors and others. Many studies using knockout mice have provided important data on the roles of these transcription factors in B cell development. For instance, Aiolos regulates immature B cell apoptosis mediated by B cell receptor signaling. Helios regulates the gene expression of protein kinase Cs (PKCs). E box binding protein 2A (E2A) regulates gene expressions of survivin, IAP2 and caspase-8. Early B cell factor 1 (EBF1) dramatically regulates gene expressions of B lymphocyte-induced maturation protein-1 and PKCθ. In addition, Paired box gene 5 (Pax5) regulates gene expressions of p300/CBP-associated factor, histone deacetylase-7 (HDAC7), HDAC9, Aiolos, Origin binding factor-1 (OBF1), Ikaros, E2A, EBF1 and PU.1 dramatically and moderately. Further, Pax5 isoforms A and B differentially regulate other B cell development-related factors. These results, together with enormous previous related data, significantly contribute to the elucidation of roles of these transcription factors in normal development and differentiation of B cells.