Background: Thromboembolic events (TEEs) are serious complications leading to significant morbidities and mortality in cancer patients (pts). Although incidences of 7-17% for TEEs were reported in non-small cell lung cancer (NSCLC) pts undergoing palliative chemotherapy, there were few reports on TEEs in NSCLC pts receiving immune checkpoint inhibitor (ICI) monotherapy. Methods: This study retrospectively analyzed 232 pts with stage III/IV or recurrent NSCLC who initiated palliative ICI monotherapy (1^st line: 52, ≥2^nd line: 180) from September 2017 to August 2022 in a single center. TEE occurrences were confirmed in pts during ICI treatment or within 6 months post-completion, while TEEs after regimen change were excluded. Results: Pembrolizumab (107 pts) was the most frequently administered agent, followed by atezolizumab (63 pts) and nivolumab (62 pts). TEEs were identified in a total of 14 pts (6.0%), and pulmonary thromboembolism was the most common type of TEEs (7 pts). No significant risk factors associated with TEE occurrence were identified, including age, performance status, Khorana score, type of drugs, and the line of chemotherapy. Conclusions: TEEs occurred at a relatively lower incidence in NSCLC pts receiving ICI monotherapy compared to previous studies involving cytotoxic chemotherapy, particularly platinum-based regimens. Nevertheless, the incidence is non-negligible and careful monitoring for TEEs in NSCLC pts undergoing ICI monotherapy is needed.