In acute phase of ischemic stroke, as neuroprotective and neurogenerative role of granulocyte-colony stimulating factor(G-CSF), anti-apoptotic action, anti-inflammatory and anti-immune effect, and brain protective action against excitatory neurotoxicity have been reported. Several clinical trials in ischemic stroke patients using G-CSF have been carried out and reported the safety, improvement of clinical symptom, and reduction of infarct volume. But the efficacy of G-CSF administration in acute ischemic stroke has not been well proved. Further clinical studies with more patients, more uniform infarct size, and similar distributions of stroke subtype, are needed to clarify its effectiveness. Combined therapy with G-CSF and thrombolysis will be also expected as the next step of clinical trials.