Objective: To investigate the relationship between ABCG2 expression induction and chemoresistance of gemcitabine in pancreatic cancer cells. Methods: The inhibition ratio of the pancreatic cancer SW1990 cells was measured by CCK-8 assay after exposure to different concentrations of gemcitabine for different time periods, and the half maximal inhibitory concentrations (IC50) of gemcitabine for SW1990 cells at different incubation times were determined. SW1990 cells were exposed to a proper concentration of gemcitabine chosen according to the IC50 values for 24, 48 and 72 h respectively, and then, the apoptosis rates of the cells were examined by flow cytometry, and the protein and mRNA expressions of ABCG2 were detected by Western blot and RT-PCR, respectively. Results: The proliferation of SW1990 cells was significantly inhibited by gemcitabine treatment, in a concentration- and time-dependent manner, but the IC50 value of gemcitabine showed a time-dependent increase (all P<0.05 ). After exposure to 3.9 mg/mL gemcitabine for 24, 48 and 72 h, the total apoptosis rate of SW1990 cells was gradually increased but their late apoptosis rate showed a decreasing trend; both protein and mRNA expressions of ABCG2 in SW1990 cells were significantly elevated in a time-dependent manner (all P<0.05). Conclusion: Gemcitabine can inhibit the growth of pancreatic cancer SW1990 cells, but its effect weakens with time, which may probably be associated with the up-regulation of ABCG2 expression induced by gemcitabine.