The mechanical properties of thin foil specimens of Types 304 and 316 austenitic stainless steels (thickness: 18 to 350 µm) have been investigated at room temperature. The 0.2% proof stress, ultimate tensile strength, work hardening exponent, and total elongation generally decrease with decreasing specimen thickness at a constant grain size. The effect of grain size on the 0.2% proof stress of the 316 stainless steel is smaller than that of the 304 stainless steel. The fracture mode of the specimens is ductile fracture and does not depend on the specimen thickness.