The relationship between solid-state morphology and heat-deflection temperature (HDT) of nucleated polypropylenes was studied. Using optical microscopy to characterize the morphology and DMTA to determine the temperature dependence of the tensile modulus, a composite model was adapted to estimate the HDT. Both compression-molded films and injection-molded HDT bars were investigated. Compression-molded films were isotropic except for a thin skin, and the temperature dependence of the tensile modulus was very similar for all compression-molded films regardless of the nucleating agent. Results on isotropic specimens could not account for the higher ASTM HDT of nucleated samples. Injection-molded HDT bars exhibited an anisotropic gradient in both the morphology and the temperature-dependent modulus. A composite model was developed to estimate the HDT. The model successfully predicted the ASTM HDT values relative to the HDT of unnucleated polypropylene. The increase in HDT was caused by the increased retention of melt orientation, due, in turn, to the higher crystallization temperature of the nucleated samples.