Targeting adverse pathogenic gut microbiota regulation through fecal microbiota transplantation (FMT) may restore health and has been validated in some aging-related diseases. However, the mechanisms of the gut microbiota's role in frailty and whether modulation of the gut microbiota can treat age-related frailty remain largely unknown. To assess the effects of FMT on frailty, we used bidirectional fecal microbiota transplantation in young and old mice. We demonstrated that fecal bacteria transplanted from old mice into young mice reduced body weight and grip strength (p=0.002), and led to elevated inflammatory factors in young mice, but had no significant effect on intestinal barrier function. Notably, FMT treatment in older mice not only improved frailty (grip strength: p=0.036, low physical activity: p=0.020, running speed: p=0.048, running time: p=0.058, frailty score: p=0.027) and muscle mass, but also improved intestinal ecological imbalances, intestinal barrier function, and systemic inflammation (serum TNF-α: p=0.002, and IL-6: p<0.001). KEGG enrichment analysis of fecal metabolites showed that FMT may ameliorate frailty through the sphingolipid metabolism pathway. In addition, aged mice given FMT treatment showed a significant increase in the abundance of SCFA-producing bacteria and increased levels of short-chain fatty acids (butyric acid: p=0.084, propionic acid: p=0.028). Subsequent further verification found that FMT ameliorating frailty may be achieved through SCFAs metabolism. Another mechanism study found that FMT reduces lipopolysaccharide levels (p<0.001), thereby inhibiting the TLR4/NF-κB signaling pathway and its downstream pro-inflammatory products. Therefore, regulating SCFAs metabolism by altering gut microbial composition and targeting the gut-muscle axis with LPS/TLR4 pathways may be potential strategies to treat frailty in older adults.