ABSTRACT: Aging and unhealthy diets are risks for metabolic diseases including liver cancer. Bile acid receptor farnesoid X receptor (FXR) knockout (KO) mice develop metabolic liver diseases and progress into liver cancer as they age, and Western diet (WD) intake facilitates liver carcinogenesis in those mice. This study aimed to uncover molecular signatures within the gut-liver axis for diet and age-linked liver diseases in FXR-dependent or independent manners. Many more transcripts were changed due to WD intake and aging in WT mice than those in FXR KO mice. In other words, WD intake and aging impact the hepatic transcriptomes and metabolomes in an FXR-dependent manner. In WT mice, WD/aging upregulated inflammation-related genes and downregulated genes involved in oxidative phosphorylation (OXPHOS). Urine metabolomes provided clear distinguishing for differential dietary intake. By contrast, the metabolomes of the liver, serum, or urine could reflect age differences. Further, irrespective of differential diets intake or ages, transcriptomes, metabolomes, and cecal microbiota distinguished WT and FXR KO. Western dietary patterns and aging share molecular commonality with FXR deactivation. Notably, WD, aging, and FXR deactivation commonly altered hepatic cell division-related transcripts (Cenpe, Ect2, Top2a, Kif20a, Tpx2, Nuf2, Kif18b, Aspm, E2f8, and Hmmr), which are associated with overall survival rate in HCC patients. In conclusion, FXR is essential for maintaining metabolic homeostasis in response to WD intake and aging. FXR activation helps to alleviate diet and/or aging-induced metabolic health issues.