β-Glucan is a natural immunomodulator consisting of glucose molecules. It is a well-established modifier with significant beneficial properties in infectious diseases and cancer therapy. Glucan effects on melanoma are relatively less studied, despite the increasing incidence of this type of cancer. In the current study, we focused on possible effects of insoluble yeast-derived β-glucan on the growth of melanoma cells. We found that glucan supplementation had a strong-positive effect in both reducing tumor weight, lung colonies and overall survival rate of tested animals. In addition, glucan inhibited the damage to blood cells and potentiated the effects of regular chemotherapy. By using depletion of natural killer (NK) cells, we showed that these effects are, at least partly, mediated by direct action of glucan on NK cells.