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Objective: Tumor associated macrophages (TAM) have been characterized as a critical population of immunosuppressive cells in a variety of tumor types.B7-homologue 1 (PD-L1), has been described to exert immune regulatory functions.This study was to investigate the change of circulating PD-Ll-expressing CD68+ macrophage correlated with clinical parameters of ovarian cancer.Methods: CD68+ cell were obtained by MACS.Analysis of PD-L1 and CD40 on CD68+ cells was detected by FCM.To elucidate the functional significance of CD40 in upregulation of PD-L1 expression on CD68+ macrophage, we performed culture experiments of the PD-L1low CD68+ cells in the absence or presence of sCD40L.Results: we showed that a fraction of macrophages in ovarian tumor over-expressed PD-L1 molecule.Macrophages would be induced to express PD-L1 molecule by sCD40L treatment.Interestingly, frequency of PD-Ll-expressing macrophage (CD68+ cells) in peripheral blood from ovarian cancer patients was significantly higher than that of benign ovarian disease and healthy, thereafter related to TNM stage.Conclusions: The CD40 activation mediating up-regulation of PD-L1 expressing on TAM represents a novel immune escape mechanism which links the pro-inflammatory response to immune tolerance in the tumor milieu, PD-L1+macrophages constitute a novel suppressor cell population in ovarian cancer.