Background: Programmed death 1 (PD-1)/ PD-L1 pathway is a negative feedback mechanism that suppresses the activity of T cells. Some previous studies showed that positive PD-L1 expression on tumor cells (TC) was poor prognostic factor in patients with colorectal cancer; however, recent studies suggest that IC also play important roles to determine the prognosis in cancer patients. The aim of this study is to investigate the association of clinical and pathological features with PD-L1 expression on TC and IC. Methods: We retrospectively reviewed data of consecutive patients with stage IIIb colorectal cancer (Japanese classification of colorectal carcinoma The 8^th Edition), who underwent surgery and received adjuvant chemotherapy in our institution between January 2009 and July 2012. PD-L1 expression was evaluated by immunohistochemistry (IHC) on TC and IC. Specimens were scored as IHC low (L) or high (H), if < 5% or ≥ 5% of cells were PD-L1 positive, respectively. Results: Seventy-four patients were included in this analysis. Median age was 61 years (range 32-84). Thirty-one (41.9%) and 43 (58.1%) patients received fluoropyrimidine and fluoropyrimidine combined with oxaliplatin as adjuvant chemotherapy, respectively. The median follow-up time was 51.3 months (range 4.6-75.9). The number of patients with PD-L1 expression on TC/IC (H/H, H/L, L/H, and L/L) were 0, 12, 11, and 51, respectively. The median disease-free survival (DFS) in patients with high and low PD-L1 expression on TC were 29.9 months and “not reached”, respectively (hazard ratio [HR] 2.02; 95% confidence interval [CI], 0.85-4.30; P = 0.11). The median DFS in patients with high and low PD-L1 expression on IC were “not reached” and 55.1 months, respectively (HR 0.29; 95%CI, 0.05-0.95; P = 0.04). Conclusions: Although high PD-L1 expression on TC is associated with poor prognosis, high PD-L1 expression on IC positively affects the survival in patients with stage IIIb colorectal cancer.