Molding tobacco filters having a variety of cross-sections which are practically useful in providing various preferable effects such as improvement in pressure drop, balanced adsorption of smoke component or the like, are provided according to a method which is characterized in forming fiber bundles of composite fibers consisting of a first and a second component by themselves, or a mixture of at least 20% by weight (based upon the total fiber mixture) of said composite fibers and another kind of fibers so as to give a variety of cross-sections to said fiber bundles, and subjecting said fiber bundles to heat-treatment at a temperature lower than the melting point of the first component but higher than the melting point of the second component to stabilize the structure by the self-adhesion of the second component; the first component of a fiber forming polymer and the second component consisting of one or more kinds of polymer having a melting point lower than that of the first component by 10.degree. C. or more, being disposed in side-by-side or sheath and core relationship so as to give a circumferential ratio of 50.about.100% of the fiber cross-section.