The bursa of Fabricius is an acknowledged central humoral immune organ unique to birds， which is vital to B cell differentiation and antibody production. However， the function and mechanism of the biological active peptide isolated from bursa on B cell development and autophagy were less reported. In this study， we isolated a new oligopeptide with nine amino acids Leu-Met-Thr-Phe-Arg-Asn-Glu-Gly-Thr from avian bursa following RP-HPLC， MODIL-TOP-MS， and MS/MS， which was named after BP9. The results of immunization experiments showed that mice injected with 0.01 and 0.05 mg/mL BP9 plus JEV vaccine generated the significant increased antibody levels， compared to those injected with JEV vaccine only. The microarray analysis on the molecular basis of BP9-treated immature B cell showed that vast genes were involved in various immune-related biological processes in BP9-treated WEHI-231 cells， among which the regulation of cytokine production and T cell activation were both major immune-related processes in WEHI-231 cells with BP9 treatment following network analysis. Also， the differentially regulated genes were found to be involved in four significantly enriched pathways in BP9-treated WEHI-231 cells. Finally， we proved that BP9 induced the autophagy formation， regulated the gene and protein expressions related to autophagy in immature B cell， and stimulated AMPK-ULK1 phosphorylation expression. These results suggested that BP9 might be a strong bursal-derived active peptide on antibody response， B cell differentiation， and autophagy in immature B cells， which provided the linking among humoral immunity， B cell differentiation， and autophagy and offered the important reference for the effective immunotherapeutic strategies and immune improvement.