Crystal growth of a sillenite structure with a composition of Bi 12(Si1-xTix)O20 and the corresponding optical characteristics have been systematically examined. The incongruent melting materials Bi12TiO20(BTO) have been observed to form a solid solution with congruent melting materials Bi 12SiO20(BSO) for the whole range of the x value. The cutoff wavelength increases and the optical activity decreases linearly with BTO content in the crystals. The photorefractive effect is modified significantly due to the addition of BTO. The diffraction efficiency (η) of the photorefractive grating increases first with BTO content for x≤0.33 and saturates for a larger amount of BTO addition. The response speed is, however, promoted markedly for x≥0.48.