Abstract: Objective To explore the effects of calcium pump inhibitor thapsigargin (TG) on intracellular Ca²⁺ and the expression of caspase-3 protein in mouse lung fibroblast. Methods Mice lung fibroblast cells were divided into three groups: the blank control group, transforming growth factor-β₁（TGF-β₁） group and TG treated group. The cells were induced by 5 ng/mL TGF-β₁ for 24 h in TGF-β₁ group and TG group, 4 μmol/L TG was added in TG group for 24 h. After 48 h, the cells were collected, and the cell structure was observed by transmission electron microscope, intracellular Ca²⁺ level was detected with laser confocal microscope, the protein expression of caspase-3 was examined using immunohistochemistry method. Results Transmission electron microscopy showed that the cells in the blank control group had obvious nucleolus, complete organelles and less apoptosis. In TGF-β₁ group, the cell morphology was intact, chromatin was evenly distributed, and no apoptotic cells were found. In TG group, there were a large number of apoptosis of fibroblasts, chromatin clumps in nuclei and a small amount of collagen fibers. The level of Ca²⁺ in TGF-β₁ group was significantly lower than that in control group (P<0.05), and which in TG group was significantly higher (P<0.05 ). The protein expression of caspase-3 in TGF-β₁ group were significantly lower than that in blank control group (P<0.05), which in TG group increased obviously (P<0.05).Conclusion TG could cause intracellular calcium dysregulation in mouse lung fibroblasts, increase caspase-3 protein expression and promote cell apoptosis.