In this letter, the one-twelfth mode of equilateral hexagonal substrate integrated waveguide (TMSIW) is proposed for the first time. Comparing with traditional substrate integrated waveguide (SIW), the size of TWSIW is only 1/12 which is reduced 11/12 while the resonant frequency of TWSIW is almost unchanged. Loading a complementary split-ring resonator (CSRR) structure, the miniaturization is further improved and the filter selectivity is improved. The filter design uses two of TWSIW which is connected with a microstrip line. The structure is not complex, easy to process, low loss, and the passband has a certain bandwidth. After processing and testing, it shows that the measurement results of filter give good agreement with the simulation results. This filter has advantages in all indexes by comparing with other works.