The current study investigated the effects of the granulocyte-macrophage colony-stimulating factor (GM-CSF) on rat endothelial progenitor cell (EPC) biology. EPCs were isolated from rat bone marrow and experiments were carried out to determine the dose- and time-dependent effects of GM-CSF on angiogenesis, proliferation, viability, migration and vasculogenesis. EPCs were co- cultured with rat cardiac microvascular endothelial cells (CMECs) to determine the effect of GM- CSF on EPC angiogenesis in vitro. EPC proliferation and viability, migration, and vasculogenesis were measured by the respective application of the method of transcription and translation (MTT) assay, the Transwell chamber assay and the Matrigel assay. GM-CSF treatment stimulated EPC angiogenesis, proliferation, viability, migration and tubule formation in a dose- and time-dependent manner. Furthermore, GM-CSF treatment led to the upregulation of integrinβ2, vascular endothelial growth factor (VEGF) and p-extracellular signal-regulated kinase (p-ERK) 1/2 levels in EPCs. Moreover, two different phosphatidylinositol 3-kinase (PI3K) inhibitors (LY294002 and Wortmannin) partially inhibited the GM-CSF-mediated increase in p-ERK1/2 levels in EPCs. The ERK inhibitor, FR180204, dramatically inhibited GM-CSF-mediated stimulation of EPC proliferation, migration and vasculogenesis. Taken together, the results of the current study provide evidence that a PI3K-dependent ERK signalling pathway is, at least, partially responsible for the GM-CSF-mediated effects on EPC function.