This paper presents the influence of Reynolds number on propeller open-water performance at the towing tank and the cavitation tunnel for series propellers(No. of blade=4, $0.3{leq}A_E/A_O{leq}0.75,;0.5{leq}P/D{leq}1.1$). It is shown that the Reynolds number recommanded by 15th and 17th ITTC is not large enough to obtain reliable P.O.W. test results and then the suitable test conditions for the both facilities is suggested. The correlation of the propeller open-water characteristics at the cavitation tunnel and the towing tank is described and a correlation factor $kappa$ is deduced from those test results. The viscous effect of the flow around the propeller shaft on the propeller characteristics is investigated from the velocity measurement by Laser Doppler Velocitimetry(L.D.V.). The measured velocity distribution shows that viscous flow effect is not negligible.