Lauric acid (LA) has the possibility to improve milk production in dairy cows by improving mammary gland development, however, the mechanism by which it might regulate mammary gland development is unclear. The influence of LA on milk production, nutrient digestibility and the expression of proteins related to mammary gland development in dairy cows were evaluated. Forty primiparous Holstein dairy cows were divided into 4 groups in a randomized block design. Four treatments included the control (0 g/d LA per cow), low-LA (100 g/d LA per cow), medium-LA (200 g/d LA per cow), and high-LA (300 g/d LA per cow). Yields of milk, fat-corrected milk, and energy-corrected milk quadratically increased (P < 0.05), and yield and content of milk fat linearly increased (P < 0.05) with LA supplementation. Percentages of C12:0, C18:1 and C20:1 fatty acids in milk fat linearly increased (P < 0.05), but that of C16:0 fatty acid linearly decreased (P = 0.046). Supplementation of LA led to a linear and quadratical increase (P < 0.05) in digestibility of dry matter, organic matter, neutral detergent fibre and acid detergent fibre, and ruminal total volatile fatty acid concentration but a linear reduction (P = 0.018) in the ratio of acetate to propionate. The enzymatic activities of ruminal pectinase, xylanase, and α-amylase, and populations of total bacteria and anaerobic fungi increased linearly (P < 0.05), while populations of total protozoa and methanogens decreased linearly (P < 0.05) with increased LA addition. Following LA addition, blood glucose, triglyceride, estradiol, prolactin, and insulin-like growth factor 1 concentrations increased linearly (P < 0.05) and albumin and total protein concentrations increased quadratically (P < 0.05). Moreover, addition of 200 g/d LA promoted (P < 0.05) the expression of protein involved in mammary gland development and fatty acids synthesis. These results suggested that LA addition enhanced milk production and fatty acids synthesis by stimulating nutrient digestion, the expression of proteins associated with milk fat synthesis and mammary gland development.