A research on the influence of resonator length on the performance of a standing wave thermoacoustic prime mover has been conducted. The thermoacoustic prime mover consists of an electric heater, a resonator tube filled with atmospheric air, and a stack. The stack was made of stainless steel wire mesh screens with mesh number of #14. The stack had a length of 5cm and placed 13cm from resonator hot-end. The resonator tube was made of stainless steel pipe with 6.8cm inner diameter. The electric heater which has a maximum power capability of 299W was attached to the hot side of the stack. We varied the resonator length from 105cm until 205cm. It was found that the thermoacoustic prime mover with a resonator length of 155cm generated the sound with the smallest onset temperature difference and shortest time to reach the onset condition, those are 252 °C and 401 s, respectively. Also, the prime mover with a resonator length of 105cm produced the highest frequency that is 174Hz. On the other hand, by using resonator length of 180cm, the prime mover generated the highest pressure amplitude of 0.0041MPa, and the thermoacoustic device delivered the highest acoustic power of 2.8W and efficiency of 0.9%.