Breast cancer metastasis to the brain is an increasing problem. In patients with advanced breast cancer, up to 30% have brain involvement. We have isolated a variant (4T1Br4) from the 4T1 syngeneic mouse model of triple negative breast cancer that metastasises preferentially to the brain, in up to 80% of mice. Affymetrix gene array profiling identified the serine/threonine survival kinase PIM-1 to be upregulated in brain metastatic tumours compared to tumours derived from parental or other related highly metastatic variants of the 4T1 model. Here, we confirmed the high expression of PIM-1 mRNA and protein in mouse and xenograft models of breast cancer metastasis to brain by qRT-PCR and immunohistochemistry. We show that PIM-1 mRNA expression correlates with the brain metastatic propensity of mouse and human breast cancer cell lines. Furthermore, we demonstrate that high expression of PIM-1 in brain-metastatic cells is associated with increased resistance to conventional chemotherapy. Accordingly, pharmacological inhibition of PIM-1 or its stable downregulation by shRNA restores chemosensitivity. We have explored the mechanism of resistance by assessing changes in the level and activity of the P-glycoprotein (Pgp) efflux pump in response to PIM-1 inhibition.. Furthermore we have found that PIM-1 expression correlates with increased GLUT-1 glucose transporter expression, indicating that PIM-1 may play a role in the regulation of cellular glucose metabolism. We propose that PIM-1 may be a useful prognostic factor and therapeutic target for the treatment of brain-metastatic breast cancer.