© 2014 SPIE. A critical electromagnetic response of a self-complementary structure was investigated. The nearly perfect selfcomplementary checkerboard patterns were fabricated by the electron-beam lithography and their electromagnetic responses are measured in the terahertz region. The electromagnetic responses are affected drastically by the small structural difference even though the differences are less than 0.1% of the wavelength of the incident electromagnetic waves. The sample most close to the self-complementary checkerboard pattern shows a less frequency dependent response, which is expected for the self-complementary structures. In this sample, the metallic squares seem to be connected randomly from the SEM observation. The effect of the structural randomness in metal mesh structures is also investigated to obtain the common electromagnetic properties in randomly connected systems.