Objective To explore the expression changes of α and β1 subunit protein and mRNA of the large-conductance calcium-activated potassium channels (BK Ca) in mesenteric arterial smooth muscle cells of type 2 diabetes mellitus (T2DM) rats, and to elucidate the specific mechanism of BK Ca channel activity in T2DM mesenteric arterial smooth muscle cells from the molecular level, and to provide new targets for the comprehensive treatment of T2DM and the experimental basis for the specific needle to the drug research and development. Methods After one-month high glucose and high fat diet, SD rats were treated with intraperitoneal injection of streptozotocin (STZ 25 mg/kg) to establish a rat model of type 2 diabetes mellitus. Western blot and real-time PCR were used to detect α and β1 subunit protein and mRNA expression levels. Results Western blot showed that α subunit protein expressions of mesenteric artery BK Ca channel in model group at 8 and 12 weeks were (1.093 ± 0.251) and (0.921 ± 0.153)respectively, and had no statistical significance compared with the control group (P > 0.05). Expressions of β1 subunit protein in model group at 8 and 12 weeks were (0.334 ± 0.200) and (0.193 ± 0.310) respectively. There was statistical significance compared with the control group (P < 0.05). Real-time quantitative PCR results showed that α subunit mRNA expressions of mesenteric artery BK Ca channel in model group at 8 and 12 weeks were (1.15 ± 0.03) and (0.92 ± 0.04), and had no statistical significance compared with the control group (P > 0.05). Expressions of β1 subunit mRNA were (0.47 ± 0.10) and (0.37 ± 0.12), which were significantly reduced comparing with the control group (P < 0.05). Conclusions Expressions of β1 subunit protein and mRNA of BK Ca channel in mesenteric artery are decreased significantly in T2DM rats at 8 and 12 weeks.