Background: This study aimed to investigate the immune microenvironment features and efficacy of PD-1/PD-L1 blockade of NSCLC with insertions in exon 20 (Ex20ins) of EGFR or HER2.Methods: Molecular spectrum, tumor mutational burden (TMB), PD-L1 protein expression, and the abundance of CD4+ and CD8+ tumor-infiltrating lymphocytes (TILs) were reviewed for NSCLC patients with Ex20ins of EGFR or HER2. Results: Thirty-five patients carrying EGFR Ex20ins and 21 patients harboring HER2 Ex20ins were retrospectively enrolled between April 2016 and September 2018. The average TMB was 3.3 mutations/megabase. PD-L1 expression in patients with EGFR Ex20ins was significantly higher than those with HER2 mutations (48.6% vs. 19.0%, P=0.027). High TMB and PD-L1 expression was independently associated with considerably poor prognosis (P=0.025, P=0.045; respectively). Finally, patients harboring EGFR Ex20ins seemed to be sensitive to PD-1/PD-L1 blockage whereas it showed limited efficacy in patients with HER2 Ex20ins. Conclusions: NSCLC patients with EGFR/HER2 Ex20ins had distinct immune features. Patients with EGFR Ex20ins had significantly higher PD-L1 expression than those with HER2 mutations, which may be the underlying reason for the different responses to PD-1/PD-L1 blockage.