Nasal air flow and temperature were analyzed using a voxel model constructed directly from medical images. The nasal cavities of a healthy male were reconstructed using CT slices in the axial direction at an image resolution of 0.488 mm/pixel and a slice interval of 0.40 mm. The rough surfaces in the image, which were caused by the resolution, were smoothed using a bilinear interpolation algorithm. A voxel-based simulation of inspiratory flow was then performed with a voxel pitch of 0.20 mm. With an interpolation image resolution of 0.163 mm//pixel, the voxel model successfully simulated an overall pressure drop and airflow temperature to the same extent as the conventional boundary-fitted model.