Background and purpose: Pancreatic cancer is one of the most deadly human malignant neoplasms. Resistance to chemotherapeutic drugs is a major reason responsible for poor prognosis in the treatment of pancreatic cancer patients. MicroRNA (miRNA

miR) is a family of small non-coding RNA molecules

dysregulated miRNA is associated with various tumor biological function. miR-33a has been widely reported as a metabolismrelated miRNA

while its relationship with drug resistance has little understand. This study was focused on the effect of miR-33a on gemcitabine chemoresistance in pancreatic cancer to bring the novel theoretical basis to chemotherapy for pancreatic cancer. Methods: In situ hybridization and Real-time PCR were used to analyze the miR-33a expressions in pancreatic cancer tissue sample and cell lines

respectively. Cell counting kit 8 (CCK-8) assay was used to calculate the IC50 value of different pancreatic cancer cells. Results: miR-33a was down-regulated in pancreatic cancer tissue and cell lines compared with para-cancerous tissues and normal HEK293T cells. Moreover

miR-33a over expression not only could enhance the chemosensitivity to gemcitabine in pancreatic cancer cells

but also rescue the gemcitabine resistance in pancreatic cancer cells. Conclusion: Down regulation of miR-33a in pancreatic cancer decreases the chemosensitivity to gemcitabine

resulting in development of acquired gemcitabine chemoresistance. It provides the theoretical basis to develop a new molecular targeted drug to combine with chemotherapy for pancreatic cancer.