The standard enthalpies of formation and strain energies for a series of homocubanes have been investigated by high-level ab initio G3(MP2)/B3LYP method. The relative stabilities of isomers are discussed. The comparison is made between the results of ab initio and molecular mechanics methods with the aim of assessing their performances. The usefulness of high-level calculations for generating thermochemical databases of relatively large molecules (e.g. C11H14) was also demonstrated.