Various structural possibilities for SinC and SinC2 (n = 1-7) neutral and anionic isomers were investigated using the second-order Moller-Plesset (MP2) approximation at the 6-311+G(d) level. The calculations predicted the existence of a number of previously unknown isomers (i.e., Si5C2 and Si6C2). We found that the basis set [6-31G(d)] with the MP2 approximation was too small to explain the photoelectron spectra of Si,C. clusters reasonably. Our present results agree satisfactorily with the photoelectron spectroscopy. The strong C-C bond is no longer the dominant factor in the building-up principle of mixed Si6C2 neutral and anionic clusters. The calculated adiabatic electron affinities in their ground states showed that SinCm (n + m = 3, 6) clusters are more stable than any others in SinC and SinC2 (n = 1-7) species, being consistent with the observed TOF signal intensities. Their stability tends to decrease with the increase in the size of these clusters.