Jak1/2 inhibitor ruxolitinib is a promising agent for treating steroid-refractory GvHD after allogeneic hematopoietic stem cell transplantation (SCT) to produce quick and durable responses. However, optimal dose and tapering schedule of ruxolitinib remain to be determined. Discontinuation of ruxolitinib in myelofibrosis often induces 'withdrawal syndrome' characterized by acute relapse of the disease, but this issue is not well addressed in the treatment of GvHD. Four patients with GvHD (one acute and three chronic) after SCT for myelofibrosis were treated with ruxolitinib. Low-dose ruxolitinib at 5 mg/day was safe and effective, but one of two patients treated at 10 mg/day of ruxolitinib was complicated with severe cytopenia. Withdrawal syndrome developed in one patient, who died of recurrence of GvHD shortly after discontinuation of ruxolitinib. Slow tapering or maintenance with low-dose ruxolitinib inhibited GvHD flare. Our experience calls attention that initiation at low-dose of ruxolitinib may be safe and careful tapering schedule is required to avoid withdrawal syndrome in patients with GvHD after SCT for myelofibrosis.