The Swedish government in the 1960th initiated “The Million Program” to build million residentialunits to cover the housing shortage between 1965 to 1975. Tjärna Ängar neighborhood in Borlängemunicipality was built during the million-program period, where these residential units became old,and the indoor environment is uncomfortable for the residents.Recently, there have been extensive energy-efficient renovations to improving the energyefficiency,indoor air quality, and thermal comfort of these buildings. The renovation project, withcooperation between Dalarna University and the local housing company (Stora Tunabyggen)started in 2015 by renovating three buildings in the Tjärna Ängar neighborhood.This study was conducted at one of these three retrofitting buildings (Kornstigen 25) to investigatethe thermal comfort in the building following energy retrofit. The assessment of the thermalcomfort in this study is based on Fanger's model with the use of predicted mean vote (PMV) andpredicted percentage of dissatisfied (PPD) to assess the obtained measurements.An online questionnaire survey with building occupants was conducted to give a betterunderstanding of the current situation of the retrofitting building before and after the renovationregarding thermal comfort. Based on the measurement, the thermal sensation of the occupants isslightly cool according to the standard’s sensation scale during the period of the measurement. Anonline questionnaire survey assures that the occupants were feeling slightly cool during someperiods of the day inside the apartments.