The use of biogas by a cogeneration system (CGS) is a promising technology as an efficient method of energy utilization. Sewage treatment plants (STPs) are facilities that have been continuously producing biogas, and therefore the potential of application of a biogas-fuelled CGS in an STP is estimated to be very high. However, there have been few reports on efficient utilization of biogas by a CGS, especially in cold regions. Since ambient temperature in a cold region is low and varies greatly, heat demand in the STP is also great and varies greatly throughout the year. Thus, auxiliary components such as a boiler, heat pump and gas storage system are also required to cover the total heat demand throughout a year. In the present study, adopting an actual STP in a cold region and a micro gas turbine as the CGS prime mover, performance of a biogas-fuelled CGS was investigated. The performances of four possible arrangements of the CGS with different auxiliary components were compared to the performance of a conventional system. It was found that all CGS arrangements could cover the total heat demand by only using biogas produced in the facility. The CGS arrangements could reduce electrical power demand by 23∼31%, recover 74∼78% of the energy of biogas produced, and utilize almost 100% of the biogas. The CGS arrangements with a heat pump were more efficient than the CGS arrangements with a boiler. CGS arrangements that include a gas storage system will enable efficient utilization of biogas and recovered exhaust heat.