This paper describes the propeller noise reduction of the newly built supporting ship “Yokosuka” for the 6500 m deep submergence research vehicle. Propeller noise is one of the main underwater radiated noise sources and it was very important technical item to reduce the propeller noise below the required level drastically. So both improvement of the propeller shape and optimization of the CPP blade angle-revolution number combination were investigated widely from a viewpoint of minimizing cavitation occurrence at various operating conditions. Tip unloaded skew CPPs were finaly designed, making noise measurements of model propellers in the cavitation tunnel and theoretical calculations by the propeller lifting surface program. The full scale propeller noise was measured at her sea trial and compared with the predicted noise. It was found that noise levels of the full scale propller were very low and sufficiently satisfied the required noise level and our method was very effective in designing a low noise propeller.