Background/Aims: Long non-coding RNAs (LncRNAs) have been validated to be pivotal mediators in multidrug resistance (MDR) of various cancers. This study aims to explore the roles and molecular mechanisms of linc00518 implicated in chemoresistance in breast cancer. Methods: Expressions of linc00518, miR-199a and MRP1 were evaluated by RT-qPCR or western blot. IC50 values of adriamycin (ADR), vincristine (VCR) and paclitaxel (PTX) were determined by XTT assays and cell apoptosis was assessed by flow cytometry. Luciferase reporter and RIP assays were employed to detect the interaction of linc00518, miR-199a and MRP-1. Results: linc00518 expression increased nearly 2 fold and MRP1 level elevated about 2.5 fold in breast cancer tissues as compared to that in adjacent normal tissues. Also,... almost 2 fold upregulation of linc00518 and MRP-1 expressions was observed in MCF-7 cells than in MCF-10A cells. Additionally, linc00518 level was almost 2.5 fold higher and MRP1 level was about 2 fold increased in ADR-resistant MCF-7 cells (MCF-7/ADR) than in parental cell line MCF-7. Linc00518 knockdown enhanced chemosensitivity to ADR, VCR and PTX, and boosted ADR-, VCR- and PTX-induced apoptosis in MCF-7/ADR cells. miR-199a inhibitor conferred chemoresistance to ADR, VCR and PTX in MCF-7/ADR cells, and suppressing miR-199a reversed multi-drug susceptibility induced by linc00518 knockdown. Furthermore, linc00518 could act as a molecular sponge of miR-199a to repress MRP1 expression. MRP1 depletion increased the sensitivity of MCF-7/ADR cells to ADR, VCR and PTX, and this effect was attenuated following miR-199a inhibition or linc00518 overexpression. Also, linc00518 silencing increased ADR-mediated anti-tumor effect in vivo. Conclusions: linc00518 downregulation reduced MDR by regulating miR-199a/MRP1 axis in breast cancer.