The present study aimed to determine the effect of oral β-glucan on mucositis and leukopenia in 62 consecutivepatients with colorectal cancer treated with an adjuvant FOLFOX-4 regimen. The patients were retrospectivelyevaluated in 2 groups: one group received β-glucan and the other did not (control group). Leucocytes, neutrophils,and platelets were evaluated before and 1 week after chemotherapy and oral mucositis and diarrhea were noted.Leucocyte and neutrophil counts after chemotherapy in the β-glucan group were 7,300/mm3 and 3,800/mm3,respectively, and the reductions, as compared to baseline, were not significant (p=0.673 and 0.784). The medianplatelet count was 264,000/mm3 after chemotherapy in the β-glucan group and the reduction, as compared tobaseline, was borderline significant (p=0.048). In the control group, reduction in leucocyte, neutrophil, andplatelet counts was statistically significant. Oral mucositis and diarrhea were less common in the β-glucan group.We conclude that β-glucan can be used to reduce the adverse effects of chemotherapy.