ABSTRACTB cells play a crucial role in autoimmune diseases, as evidenced by autoantibody responses and the effectiveness of B cell‐targeted therapies. Janus kinase inhibitors (JAKi), which target downstream signaling of cytokine receptors, are potent rheumatic disease‐modifying drugs. However, besides reducing inflammation, JAKi may impact the adaptive immune system. In this study, we examined the effects of JAKi on B‐cell function using in vitro cultures and multiparameter flow cytometry. The results show a JAKi‐mediated reduction in plasma cell differentiation, primarily by inhibition of memory B‐cell stimulation and proliferation. JAKi exposure resulted in stalling R848, IL‐2, and IL‐21 stimulated B cells in an intermediate activated state with elevated naïve cells displaying increased expression of CXCR5, CD71, CD22, and CD20. In addition, the data demonstrate a moderate JAKi‐mediated reduction of B cell TNF and IL‐8 cytokine expression following stimulation. Importantly, the efficacy varied greatly between drugs; tofacitinib and upadacitinib (pan JAKi; JAK1i) exhibited the strongest impact, while baricitinib (JAK1/JAK2i) showed donor‐dependent variation, and filgotinib (JAK1i) had no effect. All JAKi, except filgotinib, inhibited IL‐2 or IL‐21‐induced STAT3 phosphorylation. Still, filgotinib demonstrated similar inhibition of phospho‐STAT5 as other JAKi following IL‐21. These findings underscore the therapeutic impact of JAKi through the modulation of B‐cell functions.