This study aimed to investigate phenotype of RP105(-) B cell subsets in patients with systemic lupus erythematosus (SLE). Flow cytometry was used for phenotyping RP105-negaive B cell subsets. Based on CD19, RP105, and CD138 expression, RP105(-) B cells consist of at least 5 subsets of late B cells, including CD19(+)RP105(int), CD19(+) RP105(-), CD19(low) RP105(-) CD138(-), CD19(low) RP105(-)CD138(int), and CD19(low) RP105(-) CD138(++) B cells. Especially, CD19(+)RP105(int) and CD19(low) RP105(-)CD138(int) B cells are significantly larger than other RP105(-) B cell subsets in SLE. By comparison of RP105(-) B cell subsets between patients with SLE and normal subjects, these subsets were detectable even in normal subjects, but the percentages of RP105(-) B cell subsets were significantly larger in SLE. The phenotypic analysis of RP105(-) B cell subsets suggests dysregulation of later B cell subsets in SLE and may provide new insights into understanding regulation of B cells in human SLE.