【Objective】 To investigate the effect of high-fat diet (HFD) on mammary gland development of pubertal mice and explore the possible underlying mechanisms.【Method】 Twenty 4-week-old Kunming female mice were randomly divided into control group and HFD group. The trial lasted for four weeks. The body weight and feed intake were recorded weekly. At the end of the trial, mammary glands were collected and weighed. The morphology and number of ducts were observed by using whole-mount and HE staining. Western blot was used to analyze the expressions of insulin-like growth factor 1 (IGF-1), proliferation related signaling pathway proteins such as protein kinase B (Akt) and extracellular regulated protein kinases (ErK), as well as inflammation related signaling pathway proteins, including toll-like receptor 4 (TLR4), c-Jun N-terminal kinase (JNK) and inhibitor of nuclear factor kappa-B kinase (IKK) in the mammary glands.【Result】 The feed intake of the HFD group was significantly lower than that of control group（P<0.05）, There was no significant difference in energy intakes between two groups. The body weight gain of HFD group was significantly higher than that of control group (P<0.05). In addition, HFD significantly increased mammary gland weight and the ratio of mammary gland weight to body weight (P<0.01). The results of whole-mount and HE staining demonstrated that the mammary gland development of HFD group mice were markedly inhibited, with significantly decreased duct number, duct density and number of terminal end buds (P<0.01). HFD significantly inhibited IGF-1 expression and the phosphorylation of Akt， Erk and IKK in mammary glands (P<0.01 or 0.05)， while significantly promoted TLR4 expression (P<0.01) and JNK phosphorylation (P<0.05). 【Conclusion】 HFD can suppress mammary gland development of pubertal mice, which might result from the inhibiton of proliferative signals and stimulation of inflammatory signals.