Abstract: A heat exchange tube useful as a reactor tube for producing ethylene and highly improved in heat transfer efficiency has fins formed on the inner surface of wall of the tube in one or a plurality of regions or all regions arranged from an inlet end of the tube to an outlet end thereof axially of the tube. The fins are positioned in a direction intersecting the axis of the tube and have a suitable pitch. The fins are formed by a projection helically extending on the tube wall inner surface around the axis or are each in the form of an annular projection circumferentially extending on the inner surface in a direction intersecting the axis at right angles therewith. The pitch of the fins, the angle of intersection of the fins with the axis and the height of the fins are suitably determined in conformity with the inside diameter of the tube.