We have discovered 22 GHz water vapor maser toward a narrow-line type 1 (NLS1) Seyfert galaxy, NGC4051. The detection of water masers in such galaxies is very rare. The Doppler-shifted maser components symmetrically straddle a component lying at about 712 km s-1. The location of each maser component is of great interest for studying galactic dynamical structures around an active nucleus. We report on preliminary results of VLA observations.