This study explored the impact of hepatic impairment on the safety and pharmacokinetics (PK) of FCN-437c, a novel dual CDK4/6 inhibitor for potential breast cancer treatment. In an open-label trial, 25 subjects (8 with mild hepatic impairment, 8 with moderate hepatic impairment, and 8 healthy controls matched for age, sex, and body weight) received a single 200-mg dose of FCN-437c. Results showed that FCN-437c was generally well—tolerated, with no serious adverse events. In mild hepatic impairment group, total FCN-437c Cmax increased by 9.5%, while AUC0-t and AUC0-∞ decreased by 4.8%. Free drug exposure increased by 24.7%, 8.4%, and 8.4%. In moderate hepatic impairment group, total FCN-437c Cmax, AUC0-t, and AUC0-∞ decreased by 16.7%, 17.1%, and 15.7%, and free drug exposure increased by 47.8%, 47.0%, and 49.6%. Overall, no clinically relevant differences in FCN-437c exposure were found between subjects with mild or moderate hepatic impairment and normal controls, but moderate hepatic impairment increased free drug exposure. Thus, no dose adjustment is needed for patients with mild hepatic impairment, but a reduced dose may be necessary for those with moderate hepatic impairment. Trial Registration: www.clinicaltrials.govidentifier NCT06620731 (retrospectively registered).