A category of the spherical granules contains two types of granules such as a filled granule and a cored vesicle. The spherical granules were counted to separate the filled granule and the cored vesicle. Ten mixed-breed dogs were separated into two groups. One was the control group, and the other was experimental DM using Streptozotocin at sub cutaneous. The experimental animals were selected if their blood glucose concentrations were over 300mg/dl.The obtained pancreases were then prepared for transmission electron microscope. To distinguish the granules, serial sections were employed. Each type of granule was counted and analyzed statistically by the Student t-test. The β -cells of the dog pancreatic islets displayed many rod-shaped secretory granules with a few that were spherical and cored vesicles. These granules were mainly located around a well developed Golgi apparatus. Whereas the granules extrusion of the cord vesicle were often observed, the extrusion of the rod-shaped granule were observed few. No extrusion of the spherical granule were observed. The granules classified as rod-shaped, spherical, and cored vesicle were counted. Mean values of the number of granules in the β -cells were counted in 50 cells in each animal. The granule number in the experimental animals was decreased. The ratio of rod-shaped granule between the control and DM dogs was approximately 6.6:1 and of the cored vesicle was 8.1:1. The ratio of both the rod-shaped and cored vesicle between the control and DM dogs was similar. Then the functional differentiation of two types of spherical granules was discussed.