Background: In stage II colon cancer, patients with many retrieved LNs have good outcomes. We previously reported that the longest diameter of retrieved LNs correlates with the number of LNs and can be used as a prognostic factor (Int J Colorectal Dis 2015). LNs can be divided into three main regions, cortex, paracortex, and medulla, and consist mainly of T cells, B cells, NK cells, and histiocytes. We studied the relations of the T-cell, B-cell area ratios, and the number of NK cells in longest-diameter LNs to the number of retrieved LNs and outcomes. Methods: The subjects were 320 patients with stage II colon cancer who underwent curative resection. One LN with the maximum long-axis diameter was selected, and was immunostained with CD3 as a T-cell marker, CD20 as a B-cell marker, and CD56 as an NK-cell marker. Positive area ratio was determined by image analysis. The number of CD56-positive cells were examined and the mean number per 0.093 mm²was calculated. The relations were evaluated with the use of Spearman’s rank correlation coefficient. The cut-off values were calculated by ROC curve analysis. Results: The number of LNs was 14.8 ± 10.4 (mean ± SD). The CD3-positive area ratio was 0.39 ± 0.08. The CD20-positive area ratio was 0.42 ± 0.10. The number of CD56-positive cells was 9.9 ± 10.1. The correlation coefficients for the number of LNs with CD3-positive area ratio, CD20-positive area ratio, and the number of CD56-positive cells were respectively -0.07 (p = 0.220), 0.05 (p = 0.360), and 0.33 (p < 0.001). The number of LNs positively correlated with the number of CD56-positive cells. The median follow-up period was 118 months. Patients with a CD20-positive area ratio of 0.43 or greater (n = 160) had a significantly better survival (HR, 0.64; 95%CI, 0.44-0.92; p = 0.015). Patients with 3 or more CD56-positive cells (n = 276) had a significantly better survival (HR, 0.57; 95%CI, 0.37-0.93; p = 0.017). Conclusions: A high number of NK cells in longest-diameter LNs was associated with a higher number of retrieved LNs, a longer LN diameter, and better survival. NK cells in the longest LNs may reflect the host antitumor immune response in patients with Stage II colon cancer.