Chemical additions of uracil (U) nucleobase to sidewall of each of representative (4,4) armchair carbon and silicon carbide nanotubes (CNT and SiCNT) were investigated based on density functional theory (DFT) calculations. All singular and hybrid models were optimized to obtain the minimum-energy structures. The evaluated molecular properties indicated the effects of U-attachment on properties of both of U and NT counterparts, in which additional evaluated atomic-scale chemical shifts indicated the role of atomic sites in the U-attachment processes. Both of U-CNT and U-SiCNT hybrids could be considered as achievable compounds; however, the aim of application could organize the achievement of which hybrid. There was one possibility of U-attachment for the homo-atomic system of CNT whereas there were two possibilities of U-attachment for the hetero-atomic system of SiCNT. Interestingly, the evaluated atomic and molecular properties indicated differences between the characteristics of U-SiCNT-1 and U-SiCNT-2 as an advantage of computational chemistry methodologies, in which the results were very much interesting for the water-solvated systems.