Serious failure of the latest high-tec equipment occurs easily due to electrostatic discharge (ESD), which is known to be often caused by electriflcation phenomena of human-body walking on the floor. On the one hand, it has widely been accepted that the ESD is difficult to happen in the high humidity environment, on the other hand this mechanism is not well understood. In order to study the electrical factors that govern the walking electrification in the high humidity environment, we measured electrical parameters (capacitance: C_s, resistance: R_s) of the commercially available shoes having synthetic rubber soles that determine the potential of the human body walking on a metal plate. As a result, we found that an equation of "C^ε _sR_s= constant" holds regardless of the humidity and the power number ξ for the rubber sole shoes falls in the renge from 3 to 5, which can theoretically be explained from moisture absorption properties of the dielectric material.