The excitation spectra of SnH4 and Sn(CH3)(4) were studied theoretically by the SAC-CI (symmetry adapted cluster-configuration interaction) method. The calculated spectra agree well with the observed vacuum-ultraviolet (VUV) spectra. The results of the lowest states agree with the earlier works by Fernandez et al. In higher energy region, the earlier works have overlooked many states which constitute broad observed bands. The new assignments of the spectra up to the first ionization potential are given, and the natures of the excitations are discussed, The excitations in this energy region are primarily Rydberg in nature, though some states show a strong mixing with the valence antibonding states. The difference in the VUV spectra between SnH4 and Sn(CH3)(4) is attributed to the difference in the nodes of the t(2) sigma* antibonding orbitals.