Mast cells are of paramount importance to allergies, pathogen immune responses during infections, and angiogenesis, as well as innate and adaptive immune regulations. Beyond all these roles, mast cells are now more and more being recognized as modulators of tumor microenvironment. Notwithstanding mounting evidences of mast cell accumulation in tumors, their exact role in tumor microenvironment is still incompletely understood. In this review, we discuss the significant role of mast cells in the remodeling of tumor microenvironment by either releasing various factors after activation or interacting with other cells within tumor and, as a result, the possible role of mast cell in cancer invasion and metastasis. We also discuss recent findings that mast cells actively release microparticles, which account for the transfer of membrane-type receptor signal and regulatory molecules such as microRNAs to tumor cells and immune cells. These findings on mast cells provide further insights into the complexity of tumor microenvironment remodeling.