There are proposed an expansion molded product used as an internal material, engine cover or the like of an automobile but also a sound absorbing material, sound absorbing wall or the like in the building field and being light in the weight and excellent in not only sound absorbing property but also the surface property and mechanical strength, a web and a stampable sheet suitable for use in the production thereof as well as a method of producing the same. As a solution means, there is a method of producing an expansion molded product of a stampable sheet by uniformly dispersing reinforcing fibers, thermoplastic resin and thermal expandable particles in an aqueous medium containing a surfactant with fine foams to prepare a foamy solution, filtering the foamy solution to form a web, heating pressing and cooling the web to form a stampable sheet, heating the stampable sheet to expand the thermal expandable particles, and shaping and cooling the stampable sheet, wherein the expanded thermal expandable particles are eccentrically located toward one-side surface of the expansion molded product of the stampable sheet by removing foams by suction during the filtering and eccentrically locating the thermal expandable particles toward one-side surface of the web.