In this article, we report on theoretical absorption spectra of 3C-SiC nanocrystals with different sizes and different surface termination foreign atoms using the semiempirical PM3 localized-density-matrix method. Pronounced size dependence of the absorption spectra is clearly demonstrated. Besides size effect, the influence of the surface configurations on the optical property of SiC nanocrystals is also studied. The absorption spectra of 3C-SiC nanocrystals terminated with OH or NH2 species are calculated. Compared with H-terminated case, the absorption edge of OH-terminated or NH2-terminated 3C-SiC exhibits a significant red shift. It is also found that there are some fine structures appearing at the lower energy side of the dominant absorption peak (similar to 4.4 eV) for OH-terminated 3C-SiC nanocrystals. (c) 2005 Elsevier B.V. All rights reserved.