Anaerobic treatment of palm oil mill effluent (POME) emits various odorous chemicals. Thus, Department of Environment under the jurisdiction of the Air Division has proposed odour limit of 12 000 OU m^-3 for palm oil mills in the draft odour regulation recently. Three mills with differing effluent treatment systems were selected to carry out the odour study in order to validate the proposal. Field survey results showed that the odour emission sources in all mills exceeded the proposed odour limits However, in-field odour concentrations in treatment plant areas are well below the limit. Mill with digester tank has lowest in-field odour concentrations in treatment plant areas compared to mill with covered lagoon while open ponding has the highest readings.