This study compared the tumor immune microenvironments (TIMEs) of primary gastric cancer (PGC) and paired metastatic gastric cancer (MGC). CD4(+) and CD8(+) T-cell density and PD-L1 expression were evaluated by multiplex immunohistochemistry, DNA mismatch repair (MMR) by immunohistochemistry, and immune-related genes by RNA sequencing. Twenty-three patients who underwent surgical treatment for PGC and MGC were enrolled in this study. CD8(+) T-cell, PD-L1(+) cell, and PD-L1(+)CK(+) cell densities were significantly lower in MGC than PGC. PD-L1 positivity using a combined positive score (>= 1%) and deficient MMR were observed in 52.2% and 8.7% of PGC samples, respectively, whereas both occurred in only 4.3% of MGC samples. The most frequent TIME types were inflamed (34.8%) and adaptive immune resistance (34.8%) in PGC, and immune desert (65.2%) and immunological ignorance (73.9%) in MGC. In transcriptome analysis, the expression of the T-cell inflamed gene set and co-stimulatory gene module was down-regulated in MGC compared to PGC. The total CD8(+) T-cell density was an independent prognostic marker in both PGC and MGC (univariate P=0.002, multivariate P=0.006). Our result suggest that the TIME of metastatic tumors was less immunologically active compared to that of primary tumors in gastric cancer patients.