Objective: To investigate whether agrin, a key protein in formation of neurological synapse, is expressed in lymphocytes and activate lymphocyte through affecting the formation of immunological synapse. Methods: RT-PCR was performed to detect the expression of agrin in resting and activated lymphocyte; real time PCR was conducted to analyze the correlation between agrin expression and lymphocyte activation status; H-TdR incorporation assay was used to evaluate the effect of agrin on activation of lymphocyte; and confocal microscopy was used to identified the agrin location on membrane of lymphocyte. Results: Agrin was expressed in both resting lymphocytes and activated lymphocytes. The expression was directly correlated with status of lymphocyte activation. Lymphocyte activation was inhibited by antibody against agrin. In activated lymphocytes agrin was co-capping with CD3 molecules and this capping - like structure formation was interfered by antibody against agrin. Conclusion: Agrin plays a role in activation of lymphocyte and formation of immunological synapse.