A completely asymmetrical dual-band micro-strip filter combined with a complementary split ring resonator (CSRR) consisting of a circle and a square, and substrate integrated waveguide (SIW) is presented in this paper. The proposed design can be applied in the Industrial Scientific Medical (ISM) band. The CSRR of this completely asymmetrical filter, which has both square and circular parts, can realize two distinct passbands and shows higher out-of-band rejection than symmetrical filters; it is an asymmetrical complementary split ring resonator (ACSRR). The out-ofband rejection level between two passbands can reach 40 dB, compared to 35 dB in a circular filter and 30 dB in a square filter. The measured results are in good agreement with simulated results. key words: asymmetrical complementary split ring resonator (ACSRR); substrate integrated waveguide (SIW); dual-band filter; high out-of-band rejection Classification: Microwave and millimeter wave devices, circuits, and hardware