A sheet hydroforming method is disclosed wherein two stacked metallic sheets are clamped between a pair of upper and lower dies 10, 11 and a fluid is introduced and pressurized between mating surfaces of the metallic sheets, causing the metallic sheets to bulge into a space defined by die cavities 10b and 11b. A thru-hole 11d for introducing the fluid is formed in one of the dies so as to lead to a holding surface of the die, while a pierced hole for introducing the fluid is formed in one of the metallic sheets in a portion of the one metallic sheet which portion is in contact with a holding surface 10a (10b) of one of the dies, the pierced hole being positioned with the thru-hole 11d, then the fluid is introduced in a pressurized state between mating surfaces of the metallic sheets from the thru-hole through the pierced hole, thereby causing the metallic sheets to bulge. According to this method, a pressurized fluid can be introduced between the mating surfaces of blanks easily without leakage of the fluid. Not only the efficiency of the sheet hydroforming method but also the dent resistance of a formed part can be improved.