Despite advancements in diagnosing and treating non-small cell lung cancer (NSCLC), the prognosis remains poor. Immune checkpoint inhibitors have shown promise in enhancing survival rates. Therefore, this study aimed to investigate the safety of nivolumab administration with concurrent chemoradiation therapy (CCRT) in patients with unresectable locally advanced NSCLC. Twelve patients with unresectable locally advanced NSCLC at Kansai Medical University Hospital and Izumi City General Medical Center were enrolled from May 2018 to September 2020. They received nivolumab (360 mg) tri-weekly twice, weekly carboplatin (AUC 2 min × mg/mL) and paclitaxel (40 mg/m²) for 6 weeks, and thoracic radiotherapy (60 Gy/30 fractions), followed by maintenance nivolumab therapy (360 mg, tri-weekly) for 6 months. The primary endpoint was incidence of dose-limiting toxicities (DLTs), and the secondary endpoints included safety, response rate, progression-free survival (PFS), overall survival (OS), 2-year survival rate, and treatment completion rate. Three patients completed the protocol. Nine discontinued due directly to interstitial pneumonia (three) and pneumonia (one). Ten patients (83.3%) experienced a grade 3 or higher event, of which three (25%) experienced a grade 4 or higher event, and of these, one (8.3%) experienced a grade 5 event. Three patients experienced DLTs. Concurrent nivolumab with CCRT was tolerated in unresectable locally advanced NSCLC, which offers potential treatment benefits.