The present invention addresses the problem of providing: a method for purifying a liquid using a porous polyimide and/or polyamideimide membrane having excellent impurities (e.g., metals) removal performance which is preferably compatible with a flow rate, and also having an excellent stress, an excellent breaking elongation and the like; a method for producing a chemical solution or a cleaning solution employing the purification method; a filter medium comprising the porous membrane; and a filter device equipped with the porous membrane. A method for purifying a liquid, comprising causing a portion or the whole of the liquid to pass through a porous polyimide and/or polyamideimide membrane having communicated pores from one side of the membrane to the other side of the membrane by the action of a differential pressure between the two sides.