Poultry layer houses are mostly open house system that generally faced with flies and odour and has become nuisance factors to society and the environment. This study was aimed to determine the effectiveness of applying EM in controlling pollutant gas emission at poultry layer house. A commercial poultry layer farmwas selected. Two treatments were carried out, the control without any application of microorganisms and the treated group with commercial microorganism application. Atmospheric ammonia and hydrogen sulphide were measured using a special instrument called ‘multi-gas detector’. The levels of ammonia and hydrogensulphide were measured twice a week. Odour production cannot be completely prevented on a farm. Therefore, most odour control methods are designed to keep or dissipate odours within the farm boundary, thus minimising odour complaints from surrounding neighbours. This paper reports that applying of effective microorganisms into the manure showed some positive influence in controlling atmospheric ammonia levels.