A method of washing and sterilizing an ultrapure water production system including an ultrapure water production apparatus, an ultrapure water use point and an ultrapure water flow channel connectingthe ultrapure water production apparatus with the use point. The method is characterized by carrying out at least twice the washing and sterilizing steps involving the alkali washing step of washing at least part of the interior of the system with an alkaline solution and the sterilizing step of conducting sterilization with a sterilizing water after the alkali washing. By virtue of the washing and sterilizing steps performed at least twice, metals, organic matter, microparticles and living bacteria can be removed at high efficiency from the interior of the ultrapure water production system. Shortly after the washing and sterilization, there can be produced an ultrapure water satisfying the demanded water quality.