This study investigated the protective effects of ursodeoxycholic acid (UDCA) against PA-induced apoptosis in the MAC-T bovine mammary epithelial cell (bMEC) line by assessing the level of cell viability, oxidative stress indicators, and expression of endoplasmic reticulum (ER) stress markers. MAC-T cells were pretreated with UDCA at 25, 50, and 100 μM before exposure to PA at 300 μM. UDCA was noncytotoxic at these concentrations and significantly improved cell viability, which was reduced by PA. UDCA pretreatment notably decreased PA-induced expression of GRP78, XBP1s, ATF4, and CHOP mRNA, indicating reduced ER stress. Moreover, UDCA substantially lowered PA-induced reactive oxygen species production and dichlorofluorescein fluorescence intensities. Although PA treatment elevated GSSG levels and disrupted redox balance by decreasing both the total GSH/GSSG and reduced GSH/GSSG ratios, UDCA effectively counteracted these effects. Specifically, UDCA reduced PA-induced GSSG levels and restored redox balance by increasing both total and reduced GSH/GSSG ratios. These findings suggest that UDCA mitigates PA-induced apoptosis in MAC-T cells by enhancing redox homeostasis. Therefore, incorporating UDCA into dairy cow feed could help reduce PA-induced cellular stress and improve milk production during periods of negative energy balance.