The aim of the study was to determine greenhouse gases emission factors from fattening pigs kept on deep litter and on fully slatted floor in order to compare them. The emissions were measured from July to September 2013. The buildings were located in the farms in the neighbourhood, in the Wielkopolskie Voivodeship. Gas concentrations were measured by photo – acoustic spectrometer Multi Gas Monitor INNOVA 1312. The average value of CO2 emission factor was 105 g•day-1•kg-1 (VCO2=29%) for the deep litter and 62 g•day-1•kg-1 (VCO2=31%) for a system with a fully slatted floor. For N2O value was respectively 0.047 g•day-1•kg-1 (VN2O=31%) and 0,027 g•day-1•kg-1 (VN2O=34%). The CH4 emission factor value was respectively 0.809 g•day-1•kg-1 (VCH4=63%) and 0.715 g•day-1•kg-1 (VCH4=30%). The emission factors of researched gases were higher in deep litter fattening house, for CO2 by 69%, for N2O by 74% and for CH4 by 13% than in the building with a fully slatted floor. According to the warming potentials of greenhouse gases, rearing pigs on deep litter would emit 59% more of CO2 –equivalents.