A method of manufacturing a heat exchanger in which a laminate prepared by laminating many sheets one upon another so that the neighboring sheets may be formed with bonded portions and non-bonded portions, is expanded in such a direction that the respective sheets are spaced from each other so as to form flow channels or passages between the sheets at the non-bonded portions, and which employs the steps of printing patterns of bonded material onto the sheets, laminating the sheets, and subsequently expanding the laminate of the sheets to form the heat exchanger.