Abstract: Objective According to the differential expression of ultra-conserved RNA uc.477+ in mouse normal B cells and mouse B lymphoma cells, we designed this study order to explore the effect of uc.477+ on the proliferation of mouse B lymphoma cells. Methods Normal B cells were sorted from the spleens of C57BL/6 mice, and the expression of uc.477+ was examined by RT-PCR in normal B cells and B lymphoma cells of mouse.The uc.477+ gene fragment was inserted into the pMSCV-PIG retroviral expression vector.Overexpression plasmid 477-pMSCV-PIG and empty vector plasmid pMSCV-PIG were packaged into retroviruses via 293T to infect mouse lymphoma cells 38B9, and fluorescence microscopy and flow cytometry were used to examine infection rate.The proliferation change of the 38B9 cell line with uc.477+ over-expression and the 38B9 cell line with empty vector was examined by cell counting and cell cycle. Results The expression of uc.477+ in mouse B lymphoma cells was significantly higher than that in normal mouse B cells.Stable over-expression of uc.477+ 38B9 cell line and empty vector 38B9 cell line were successfully constructed.Proliferation ability of the uc.477+ over-expressing 38B9 cell line was more stronger than the empty vector 38B9 cell line. Conclusion The expression of uc.477+ in B lymphoma cells was significantly higher than that in normal B cells of mouse.The uc.477+ can promote the proliferation of B lymphoma cells.