Abstract: This study aimed to investigate the ameliorative effects and molecular mechanisms of dual-source collagen peptides (CP) derived from tilapia and beef tendon on D-galactose (D-gal)-induced age-related sarcopenia (ARS) in mice. A mouse model of ARS was established by intraperitoneal injection of D-galactose (500 mg/kg) once daily for 14 consecutive days. After successful modeling, the mice were given collagen peptides (1000 mg/kg) via gavage once daily for 6 weeks. To evaluate the therapeutic efficacy of collagen peptides and clarify their underlying molecular mechanisms, a series of experimental assays were performed, including behavioral assessments, body composition analysis, hematoxylin-eosin (HE) staining, quantitative proteomics, and bioinformatic analysis. The results showed that compared with the model group, the grip strength and treadmill exhaustion time of mice in the CP intervention group were highly significantly increased (P<0.01), and the motion displacement was significantly increased (P<0.05), which indicated that CP effectively restored the muscle strength and exercise endurance of ARS mice. CP did not alter overall muscle mass but significantly elevated the gastrocnemius index (P<0.05) and extremely significantly elevated the quadriceps index (P<0.001), alleviating gastrocnemius atrophy, improving the disordered arrangement of muscle fibers, and reducing collagen deposition. Quantitative proteomic analysis revealed that CP regulated the expression of 167 differentially expressed proteins in the gastrocnemius muscle, with 63 proteins up-regulated and 104 down-regulated. CP up-regulated Ndufab1, Ndufb2, Ak4 and other proteins involved in maintaining energy homeostasis, as well as Stat1, Prkcb and other proteins participating in inflammation regulation and muscle repair; meanwhile, it down-regulated Trim55, Ube2d3 and other proteins to inhibit excessive muscle protein degradation. Bioinformatic analysis indicated that CP improved D-gal-induced ARS by regulating the apelin-mediated calcium and lipid metabolism balance, the gonadotropin-releasing hormone-sex hormone-muscle axis, and the downstream pathways of the growth hormone receptor. This study confirmed that the beneficial effect of CP on ARS relies on optimizing muscle function, targeting major weight-bearing skeletal muscles, and regulating multiple signaling pathways, rather than promoting muscle hypertrophy. This study provides experimental evidence and molecular mechanisms for the intervention of ARS by food-derived bioactive peptides, and also offers a new perspective for the high-value utilization of food processing by-products.