To a homo-isotactic polypropylene (PP) was added 0 to 10 ppm of quinacridonequinone which was a beta-phase nucleating agent for PP. The structure and properties have been studied on the inflation films processed from the PPs by the water-cooling or air-cooling methods. The effect of cooling conditions on crystallization has been also studied for reference. Even PPs containing beta-phase nucleating agent do not form the beta-phase but the smectic or alpha-phase at low cooling temperature. However, compared with PP without beta-phase nucleating agent, they form the alpha-phase at lower cooling temperature and form the beta-phase in the air-cooled inflation films of beta-phase nucleating agent contents are high. Although the film properties are generally not so much affected by the addition of the beta-phase nucleating agent, the dart impact strength increases for the air-cooled films which contain the beta-phase.