Most alternating current (ac) polymer EL (electroluminescent) devices to date are based on symmetrical structure. Here novel alternating current EL devices with asymmetric structure are successfully fabricated by using a hole type polymer PDDOPV [poly (2,5-bis (dodecyloxy)-phenylenevinylene)] and an electron type polymer PPQ [poly (phenyl quinoxaline)]. We report that performance of polymer devices with heterojunction in ac operation is not so sensitive to thickness of the two polymer layers as in direct current (dc) operation. This new advantage of ac operation mode over dc means easy production and cheap facilities in large-scale production in the near future. Different emission spectra are obtained when our ac devices operate in ac mode, forward and reverse bias. Emission spectrum at reverse bias includes two parts: one is from PDDOPV, the other is from PPQ.