Properties of H2O water vapor pumping by glow discharge sputtering with a LaB6 cold cathode are studied experimentally. For the purpose of developing a new type of sputter ion pump, lanthanum hexaboride (LaB6) is applied as the cathode material on the basis of a preliminary study. The application of LaB6 as the cathode of sputter discharge was proposed at first to obtain a low outgassing wall for a plasma vacuum chamber. The experiments showed that the vacuum chamber with the LaB6 sputter coating reached a lower ultimate pressure than that without the coating. LaB6 coating by glow discharge on a stainless steel wall is effective to reduce the H2O outgassing rate of a vacuum wall as shown by mass spectrometric analysis. The pumping speed of H2O by the coated wall is estimated experimentally. Characterization of the LaB6 coated films is also made by x-ray photoelectron spectroscopy measurements.