The aim of the research was defining size and range temperature of the sewage in two small, villages sewage systems. Additionally aim was to defining influence temperature of the sewage flow from sewage system and the temperature of the atmospheric air on temperature sewage in open biological reactors of flow. The research embraced the period of 12 months from January to December the year 2011. To describe this relationship used of the multiple regression of analysis. The research performed in two small sewage systems situated on the village-commune in Nowe Brzesko and Spytkowice. Sewage systems are included in the 2000 PE (Population Equivalents). In the year period of research ascertained, that average temperature in year in small biological reactors to vary from 12,6÷12,7oC, however its range is from 5,6oC to 19,2oC. Temperature of sewage in small, villages sewage systems does not exceed 10,0oC in period ⅓ year, as indicated by the permanent cooling down. Size of sewage temperature in small sewage systems is to a much greater extent then to sewage in large, urban sewage systems. Further, the temperature of the sewage in the bioreactor has a very large extent the temperature of the influent sewage and to a ...