This paper describes the following studies carried out from a viewpoint of the propeller noise reduction of the supporting ship for the deep submergence research vehicle, using controllable pitch propellers (CPP) of the previously built supporting ship “Natsushima” : 1. Noise measurements of full scale propeller 2. Noise measurements of model propeller in cavitation tunnel 3. Theoretical analysis of CPP operating condition giving rise to minimum propeller noise From propeller noise levels in various navigating conditions measured in the full scale test, it is found that there exist optimum combinations of propeller blade angle and revolution number which bring minimum noise. This fact is very important to reduce the propeller noise of the supporting ship which is wide in the propeller operation range. The model test also shows the existence of similar optimum combinations bringing low propeller noise and that these phenomena are strongly related to the occurrence of the propeller cavitation. Theoretical analysis of the propeller cavitation occurrence conditions by use of the propeller lifting surface program proves that the above optimum combinations are in good agreement with those giving the shock free entry conditions of the propeller.