A connection stabilizing mechanism between a solid tire and a bicycle rim. The connection stabilizing mechanism includes multiple fastening members connecting a solid tire with a bicycle rim. Each of the fastening members has a plate-shaped base section engaged with the bicycle rim and an extension section inserted into the solid tire. A free end of the extension section is inserted into the solid tire. A ratio of an extension length of the extension sect ion to a tire height of the solid tire is between 1:1.5 and 1:2.6, thereby maintaining a relative position of the center of a main body of the solid tire relative to the rim. Thus, the solid tire is prevented from being detached from the rim due to excessive lateral movement of the central position of the main body of the solid tire.