Purpose: The efficacy of adjuvant chemotherapy in stage IB non-small-cell lung cancer (NSCLC) with high-risk factors remains unclear and is the focus of our study. Methods: This was a retrospective multi-center study of four academic hospitals. We analyzed 285 stage IB NSCLC patients with high-risk factors according to the 8th edition TNM classification. High-risk factors were visceral pleural invasion, vascular invasion, lymphatic invasion, lung neuroendocrine tumors, and micropapillary histology pattern. We used a Kaplan-Meier survival curve and Cox proportional hazards model to analyze recurrence- free survival and overall survival. Results: Of the 285 cases, 127 (44.6%) were in the adjuvant chemotherapy group and 158 (55.4%) were in the non-adjuvant chemotherapy group (control group). Mean follow-up was 40.2 ± 18.1 months, and median follow-up was 41.5 months. Adjuvant chemotherapy significantly reduced the recurrence risk compared to the control group (Hazards ratio, 0.362; 95% Confidence interval, 0.195-0.672; P = 0.001) and the risk of death compared to the control group (Hazards ratio, 0.155; 95% Confidence interval, 0.050-0.478; P = 0.001). A higher risk of recurrence was found with a larger tumor size and a greater number of risk factors (P = 0.012, P < 0.001, respectively). The risk of death increased when vascular invasion, smoking, or multiple risk factors were present (P = 0.043, P < 0.001, P = 0.048, respectively). Conclusion: Adjuvant chemotherapy may be useful for patients with stage IB NSCLC with high-risk factors and more relevant for patients with larger tumors and multiple risk factors.