Abstract Tumor cells released membrane microvesicles - exosomes, can stimulate inflammation through MDSC, and then promote tumor growth by activating immunosuppressive networks. MyD88 is a cytoplasmic adaptor molecule essential for inducing inflammation via the TLR receptors. Very little is known about whether tumor exosome-mediated induction MDSCs and tumor growth is regulated through MyD88. In this study, we observed that mice pretreated with tumor exosomes had a significant acceleration of tumor metastasis in the lung. Tumor metastasis correlated significantly with an increase in recruitment of more MDSCs in the lung of B6 mice pretreated with tumor exosomes. These effects were blunted when MyD88 KO mice were pretreated with tumor exosomes. MDSCs induced by tumor exosomes and isolated from WT B6 mice are also more potent in inhibition of T cell activation and induction of IL-6 and TNF-α than MDSCs isolated from the lung of MyD88 KO mice via activation of the Stat3 pathway. Our in vitro data further support that addition of tumor exosomes to bone marrow derived CD11b+Gr-1+ cells isolated from WT B6 mice results in producing more cytokines, including TNF-α, IL-6 and the chemokine CCL2, than CD11b+Gr-1+ cells isolated from MyD88 KO mice. Less CCL2 in lung was observed in MyD88 KO mice pretreated with tumor exosomes than that in WT mice. Together these data demonstrate a pivotal role for MyD88 in tumor exosome-mediated induction of IL-6, TNF-α, expansion of MDSCs and tumor metastasis.