Electroless plating has several advantages over electroplating, such as uniformity of the plated layer, corrosion resistance, and applicability to an electrically non-conductive surface. In this study, to study the effect of high pressure on both the plating rate and the surface structure of the plated layer prepared by electroless nickel phosphorus plating, we changed the pressure applied to the plating bath in the range from 0 to 400 MPa. As a result, we confirmed the reproducibility of the plating rate under the same plating conditions. It was found that the plating rate increased significantly when the applied pressure was increased from 0 to higher than 20 MPa but gradually decreased with further increase in pressure.