A stoichiometric constraint effects on Frank loop growth in β-SiC during irradiation were studied by ion beam irradiation, transmission electron microscopy, and calculation based on a kinetic model. Tilted-ion beam (5.1 MeV Si2+) was irradiated at 1000°C to induce lattice damage and to implant additional Si interstitial atoms simultaneously. Growth rate of the loops observed within the damaged region appeared to be positively correlated with the deposition rate of Si ions. Analysis based on a kinetic model showed that a small amount of deposited excess Si substantially increased the net flux of Si interstitials, which believed to govern the loop growth rate. The experimental and computational results confirm the stoichiometric constraint effect on Frank loop growth in SiC, and that availability of Si interstitial atoms determines the Frank loop growth rate in most irradiation conditions.