The aim of this study is to obtain knowledge about which cultivable bacterial species are present in indoor air in homes, and whether the concentration and diversity of airborne bacteria are associated with different factors. Measurements have been performed for one whole year inside different rooms in five homes and once in 52 homes. Within homes, a room-to-room variation for concentrations of airborne bacteria was found, but an overlap in bacterial species was found across rooms. Eleven species were found very commonly and included:Acinetobacter lowffii,Bacillus megaterium, B. pumilus,Kocuria carniphila,K. palustris,K. rhizophila, Micrococcus flavus,M. luteus, Moraxella osloensisandParacoccus yeei. The concentrations of Gram-negative bacteria in general and the speciesP. yeeiwere significantly associated with the season with the highest concentrations in spring. The concentrations ofP. yeei,K. rhizophilaandB. pumiluswere associated positively with relative humidity (RH), and concentrations ofK. rhizophilawere associated negatively with temperature and air change rate (ACR).Micrococcus flavusconcentrations were associated negatively with ACR. Overall, this study identified species which are commonly present in indoor air in homes, and that the concentrations of some species were associated with the factors: season, ACR and RH.