The structures, energies, and fragmentation stabilities of silicon oxide clusters SimOn, with m = 1-5, n = 1, 2m + 1, are studied systematically by ab initio calculations. New structures for nine clusters are found to be energetically more favorable than previously proposed structures. Using the ground state structures and energies obtained from our calculations, we have also studied fragmentation pathways and dissociation energies of the clusters. Our computational results show that the dissociation energy is strongly correlated with the O/Si ratio. Oxygen-rich clusters tend to have larger dissociation energies, as well as larger HOMO-LUMO gaps. Our calculations also show that SiO is the most abundant species in the fragmentation products.