X-ray scattering is a powerful analytical tool for evaluation of phase structure in crystallizable polymers blends. Our group has been studying crystallization kinetics and micro structure development in binary polymer blends using real-time small angle X-ray scattering (SAXS). Here we describe our research on blends of a crystallizable polymer, poly(burylene terephthalate), PBT, with an amorphous polymer, polycarbonate), PC. In prior studies, we used the same crystalline polymer blended with amorphous polyarylate, PAr. The PBT/PAr system was shown to be inisciblu at all compositions in the melt state. In the present case, PBT/PC blends are not believed to be miscible in the melt. This study was undertaken to determine whether the PBT crystallization kinetics were affected by the presence of low molecular weight PC. This is part of a larger study to investigate the effects of different molecular weights on partial miscibility and on structure development in binary polymer blends.