Characteristics of fluid dynamics and noise of a multiblade radial fan have been experimentally investigated with respect to the effects of two parameters: inner diameter and the number of blades. The inner diameter Di of 58mm gave the highest fan efficiency and pressure coefficient. Up to the critical number of blades B of 120, the greater the number of blades used the higher the fan efficiency and pressure coefficient. The optimal number of blades was found to be around 120 since the characteristics of fluid dynamics remain at a maximum even if a higher number of blades is used. Blade passage frequency tone decreases as the number of blades is increased. Sound pressure level and specific noise level are reduced as the number of blades is increased up to the critical number of blades but do not decrease further when a higher number of blades are used.