It is well known that chronic hypoxia elevates hematocrit levels to maintain oxygen supply to tissues. Although such high hematocrit levels might lead to hypertension due to an increase in blood viscosity, the morbidity rate of hypertension is reportedly lower in populations residing at high altitudes. The present study aimed to clarify how chronic hypoxia affects the cardiovascular system by direct observation of the microcirculation. Mouse dorsal skin chamber was used to observe arteriolar responses and capillary angiogenesis during 1-week exposure to hypoxia. Furthermore, total peripheral vascular resistance (TPR) was evaluated by measuring blood pressure (BP) and blood flow (BF) in rat carotid arteries before and after 1-week exposure to hypoxia. After 1-week exposure to hypoxia, TPR showed no significant difference compared with normoxic conditions. Observation of dorsal skin microcirculation after 1-week exposure to hypoxia, showed that the arteriolar diameter increased by 29% and the vascular area expanded by 37% compared with measures before hypoxia. These results suggest that the effects of high blood viscosity on TPR would be modified by inducing microvascular remodeling.