Objective：To study the expression and significance of Fcγ receptor ⅡB（FcγRⅡB） of B cells in lupus-prone MRL-lpr mice. Methods：Peripheral blood of lupus-prone MRL-lpr mice at the age of 4，8，12，20 weeks were collected and serum levels of total IgG，anti-dsDNA，anti-ribosomal P0 and anti-smRNP were detected to analyze the progression of disease. The 20 weeks old MRL-lpr mice were sacrificed and the expression of FcγRⅡB and CD69 of B cells in blood and spleen were detected. The relationship between FcγRⅡB expression and B cell activation were analyzed. Results：The serum levels of total IgG，anti-dsDNA，anti-ribosomal P0 and anti-smRNP were increased with the increase of age. Expression of FcγRⅡB of B cells in blood and spleen was decreased obviously（P＜0.05） and expression of CD69 was increased obviously（P＜0.05） in MRL-lpr mice. What’s more，the CD69 positive activated B cells up-regulated the expression of FcγRⅡB in C57BL/6 mice，and this didn’t happen in MRL-lpr mice. Conclusion：The expression of FcγRⅡB is related to the activation of B cells and altered expression of FcγRⅡB may be one of the mechanisms of B cell over-activation in lupus-prone MRL-lpr mice.