Abstract: Objective : To investigate the role of extracellular signal-regulated kinase pathway (ERK), multidrug resistance1 (MDR-1) and ribonucleoside reductase M1 (RRM1) in Gemcitabine (GEM) chemoresistance in the pancreaticcancer cell line SW1990. Methods : The GEM-resistant pancreatic cancer cell line model was constructed usinga stepwise increase in concentration gradient of Gemcitabine. Immunocytochemistry was performed to detect theexpression of ERK1/2 in the established cell lines in a semiquantitative way, and the mRNA expression of MDR-1and RRM1 in the GEM-resistant pancreatic cancer cell lines was detected by RT-PCR. MTT assay was used todetermine the IC50. Results : The established pancreatic cancer cell lines cultured in medium with GEM at differentconcentrations (0, 30, 60, 100, 150 and 200 nmol/L) were able to grow and maintain their resistance throughseveral passages. The expression of ERK1/2, MDR-1 and RRM1 were elevated according to the increasing GEMconcentration. There was a highly positive correlation between MDR-1 or RRM1 expression and GEM concentration (r=0.960,P=0.002 and r=0.966, P=0.002). The gray scale of ERK1/2 was also correlated with the expressionof MDR-1 and RRM1 (r=-0.943, P=0.005 and r=-0.883， P=0.02). At a concentration of 200 nmol/L, the gray scaleof ERK1/2, MDR-1/β-actin, and RRM1/β-actin of the GEM-resistant pancreatic cancer cell line was 164.22±13.17,1.41±0.04 and 1.45±0.18, respectively. The expression of these genes decreased synchronously after the cellswere treated with ERK1/2 signaling pathway specific inhibitor U0126 to the gray scale values of 186.85±13.14,0.23±0.02 and 0.21±0.03, respectively. Conversely, there was a tendency to decreased expression of these genesafter the cells were treated with epidermal growth factor (EGF). The gray scale values ascended to 106.55±16.45,1.5±0.07 and 1.52±0.12, respectively. The IC50 of the GEM-resistant pancreatic cancer cell lines at the concentration of 0 nmol/L and 200 nmol/L were 4.104 and 10.20, respectively. There was a decrease in the IC50 to3.26 and 4.5 after the cells were treated with U0126, and an elevation to 8.89 and 17.17 after the cells were treatedwith EGF. Conclusion : The ERK signaling pathway participates in the regulation of the expression of MDR-1 andRRM1, most likely contributing to the GEM chemoresistance in the SW1990 pancreatic cancer cell line.