Abstract Magnon spectra were measured by means of Brillouin scattering from single crystals BCVIG (Bi3-2xCa2xFe5-xVxO12). We obtained a continuous band, including the bulk mag-non peak, which has been observed by Sandercock et al. in YIG, and Liu and Zhang et al. in Bi-YIG. The measured dispersion relation of the magnon band was analysed based on the theory of dipole-exchange spin waves. This measurement also show that the spin wave stiffness constant D is much larger than that of YIG and Bi-YIG. The reason of the lager D is discussed and its dependence on the incident laser power was studied.