This study examines determinants of forced evacuation, and the changes in social isolation in forced evacuees, from the Fukushima Daiichi nuclear power plant accident. Using a unique survey conducted in temporary housing in Iwaki city, we find that around 30% of the evacuees did not have conversations with anyone in the housing and 60% could not call for help when they moved to the housing. Further, 5% did not have conversations even 2.5 years after the accident. The isolated evacuees can be classified into two types: those who had been persistently isolated since moving, such as young, introverted, and self-interested evacuees, and those who could not form a personal network in the evacuation site, like male and jobless evacuees. The poor network formation of males was aggravated in large-scale housing located near downtown.