Abstract: 【Objective】This study aimed to explore the effects of nitidine chloride（NitC）on the reduction of β-casein content in buffalo mammary epithelial cells caused by heat stress，in order to provide a theoretical basis for alleviating the negative impact of heat stress on buffalo milk quality in the actual production.【Method】The temperature-humidity index （THI）of the cowshed was recorded in the non-heat stress season and the heat stress season，and the respiratory rate and rectal temperature of the buffalo were detected to determine whether the buffalo was in a state of heat stress；milk samples were collected for milk composition analysis to investigate the effects of heat stress on the β -casein content in buffalo milk；bu-ffalo mammary epithelial cells were used as the research objects，and the buffalo mammary epithelial cells heat stress model was established by treating them at 40.5 ℃ for 24 h. LiCl and LGK974 were used to activate and inhibit the Wnt pathway respectively，and the β-casein content in buffalo mammary epithelial cells and the expression levels of genes and proteins related to β-casein synthesis were detected to explore the mechanism by which nitidine chloride alleviated the decrease of β-casein content in buffalo mammary epithelial cells caused by heat stress.【Result】Compared with the nonheat stress season，the THI in the cowshed increased and exceeded the heat stress threshold of buffaloes in the heat stress season，the respiratory rate and rectal temperature of buffaloes increased significantly（P<0.05，the same below），and the β -casein content in buffalo milk decreased significantly. Cell experiments showed that treatment with 40.5 ℃ for 24 h significantly reduced the β -casein content，cell viability，and the relative expression of Wnt2，mTOR and β -casein genes and proteins in buffalo mammary epithelial cells. Nitidine chloride treatment effectively alleviated the effects of heat stress on buffalo mammary epithelial cells and significantly increased the β-casein content，cell viability and the relative expression of Wnt2，mTOR and β -casein genes and proteins in buffalo mammary epithelial cells.【Conclusion】Heat stress reduces the β-casein content and the relative expression of β-casein synthesis-related genes and proteins in buffalo mammary epithelial cells. Nitidine chloride increases the β -casein content，cell viability and the relative expression of Wnt2，mTOR and β -casein genes and proteins in buffalo mammary epithelial cells through the Wnt/mTOR signaling pathway，alleviating the decrease in β-casein content in buffalo mammary epithelial cells caused by heat stress.