Moisture transmission rate in fabric and humidity of a diffusion layer over the fabric have been measured by weighing and by the humidity gradient procedure based on the cup method. The diffusion's law of mositure transmission was applied to the air layer in the cup, the space in the fabric, and the air layer over the fabric. The transmission coefficient of mositure in the fabric was calculated by solving the simultaneous equations. It was about 2-15 x 10-³m²/h, and the values correspond to 2-14％ of the diffusion coefficient of water vapor in air. The transmission resistance and convection coeficient of moisture on the surace of fabric were estimated to 5-8 m/h and 11-20 x 10-²h/m. The transmission resistance of mositure in fabric was about 10-30％ of the total transmission resistance of moisture of the experimental system.