We investigated the comparative gas-sensing characteristics (S) of two types of nanocrystalline SiC films, obtained by direct ion deposition. The first type, isotropic nc-SiC-3C+21R, has a structure composed of a mixture of nanocrystals of cubic and rhombohedral polytypes, while the second type, nc-SiC-27R, consists of quasi-two-dimensional layers formed from parallel surfaces of the rhombohedral polytype 27R. Gas sensitivity of the samples was measured towards O2 (5%), CO (0.1%), H2 (4%), CH4 (10%) at concentrations critical for human health or safety in air. Operating temperatures for measuring the reaction to O2, CO, CH4 were 500 ℃, and for H2 - 230 ℃. Measurements showed higher sensitivity of quasi-two-dimensional films compared to isotropic samples for all types of gases. The increase in S was: for O2 by a factor of 2, for CO by a factor of 1.83, for CH4 by a factor of 2.04, and for H2 by a factor of 1.02. In addition to the increase in sensitivity coefficient, a decrease in response time to the interaction with gas molecules and recovery time after exposure cessation were observed.