〔Abstract〕 Objective To study the expression and clinical relevance of peripheral blood myeloid-derived suppressor cells(MDSCs) in Acute B lymphoblastic leukemia(B-ALL). Methods Eighty-five patients with confirmed B-ALL and fifteen healthy controls were enrolled. Flow cytometry(FCM) was used to detect the expression of MDSCs in peripheral blood. Results The level of M-MDSCs in the un-remission group was higher than that in the remission group and the healthy control group(P<0.05).The G-MDSCs levels in the un-remission group and the remission group were higher than those in the healthy control group(P<0.05), and the levels of G-MDSCs in the un-remission group were higher than those in the remission group(P<0.05). The expression level of M-MDSCs in high-risk group was higher than that in middle-risk group(P<0.05). B-ALL patients with central invasion had significantly higher G-MDSCs than those without central invasion(P<0.05).Compared with patients with good prognosis, the level of M-MDSCs increased in patients with poor prognosis(P<0.05). In G-MDSCs, poor prognosis and intermediate groups were higher than good prognosis group(P<0.05). Conclusion The level of MDSCs in peripheral blood of patients with B-ALL may be closely related to the occurrence and development of the disease, and it has certain value for judging the prognosis of patients.