Glass-ceramics containing Pb(x)Cd(1-x)F(2) microcrystallites were prepared through heat treatment of Tm(3+)/Yb(3+)doped SiO(2)-Al(2)O(3)-PbF(2) glasses. The crystallite size was controlled by varying the heat-treatment time. By changing glass composition, two types of strong optical scattering, Rayleigh and Mie scattering modes were observed for the glass ceramics. In the case of Rayleigh scattering, the scattering region expanded to the long-wavelength side with increasing the heat-treatment time. On the other hand, in the case of Mie scattering, the region were hardly dependent on wavelength, and visible light was widely scattered. It was argued that the different scattering phenomena were caused by the different size of the crystallites or their morphogical texture. Furthermore, the glass-ceramics with strong optical scattering showed higher upconversion fluorescence intensity than the matrix glass. The mechanisms for the enhanced upconversion due to the scattering were discussed.