Inorganic aluminum berate (Al18B4O33) whisker was employed in this study to reinforce polycarbonate (PC). The composites were prepared in a single-screw extruder, followed by injection molding. The whiskers were pretreated with tetrabutyl orthotitanate prior to compounding. The tensile, dynamic mechanical, impact, and thermal properties of the composites were studied. Tensile results showed that the modulus of PC-Al18B4O33 composites increased markedly with increasing whisker content. However, the tensile stress of the composite decreased slightly with the addition of 5 wt % whisker; thereafter, it increased slowly with. increasing whisker content. Differential thermal analysis and thermogravimetric measurements showed that the glass transition temperature (T-g) and 5% weight loss temperature (T-5%) of the composite shift rapidly to lower temperature regimes with the addition of Al18B4O33 whiskers up to 10 wt %. Thereafter, the T-g and T-5% of PC-Al18B4O33 composites tended to decrease slowly with increasing whisker content. The mechanical and thermal properties of PC-Al18B4O33 composites were compared with those of PC-potassium titanate (K2Ti6O13) whisker composites. The reinforcing effect of Al16B4O33 and K2Ti6O13 whiskers on PC was discussed and contrasted.