An expansion dowel assembly is made up of an axially extending dowel body and an expansion member in contacting engagement with the dowel body. The expansion member extends in the axial direction of the dowel body and is formed by a main part and an extension part projecting axially from the main part in the insertion direction of the assembly into a borehole. The cross-sectional area of the extension part transverse to the axial direction is smaller than the adjacent corresponding cross-sectional area of the main part. The extension part is shaped relative to the main part to increase the contact area of the expansion member with the dowel body and to prevent the development of excessively high surface pressures at the front end of the expansion member.