The neutrophil to lymphocyte ratio (N/L ratio) has been reported to be related to the prognosis of various types of cancer. In particular, a high N/L ratio has been suggested to be associated with poor outcome. We investigated the changes in N/L ratio during treatment in 12 patients who had undergone surgery for colorectal cancer and were receiving postoperative adjuvant therapy with a combination of chemotherapy and polysaccharide-K (PSK). The patients were stratified into 2 groups according to the preoperative N/L ratio (cut-off ratio was 2.5): high N/L (≥2.5) and low N/L (<2.5). The changes in N/L ratio and other clinical parameters over time were investigated. In patients with a high preoperative N/L ratio, the use of postoperative PSK-chemotherapy controlled the N/L ratio at low levels. The N/L ratio tended to remain low in patients with low preoperative N/L ratios. No difference in outcome was observed between patients with high and low N/L ratios. In patients who underwent colorectal cancer surgery, postoperative adjuvant therapy with a combination of chemotherapy and PSK succeeded in controlling the N/L ratio at low levels. Further studies with more patients are required to explore the outcomes associated with changing N/L ratios.