We address the thermodynamic properties of a rotating Bose gas in a 3D space in the rapid rotation regime. In such a rotation regime, the 3D system has the shape of a flat pancake and shows exotic features that can never be found in the original system. Using the semi-classical approximation, the temperature dependence of the magnetization of rotating Bose gas is investigated. In the degenerate limit, the system does not show a Bose-Einstein condensation (BEC) phase transition at a definite transition temperature. However, it exhibits a large Landau diamagnetism at low temperatures, which diminishes as the speed of rotation decreases. Our findings are compared with the previous results.