To obtain highly transparent isotactic polypropylene (PP) sheet by an industrial process, the influences of the isotacticity and metallocene linear low-density polyethylene (L-LDPE) as crystallization control material were analyzed. The sheet samples were extruded by using a direct single-belt process. Even if the sheeting was carried out under the same conditions, the lower tacticity PP generated the less and the smaller size of spherulites. Low-tacticity PP showed improvement on transparency by heat treatment as well as the high-tacticity PP. Moreover, the behavior of transparency was investigated by 10 wt% addition of various L-LDPE with wide range density. Thanks to the fine distribution particles of L-LDPE in PP matrix, the number of generated spherulites and the growth rate of them were restrained. In the case of addition of L-LDPE with the specific density to PP, the transparency was markedly improved by the heat treatment. According to the density of added L-LDPE, the suitable heat-treatment temperature condition, which showed the best transparency, was changed. This phenomenon could be explained by the refractive index difference of PP matrix and the fine distribution particles of L-LDPE. POLYM. ENG. SCI., 51: 1068-1077, 2011. (C) 2011 Society of Plastics Engineers