The purpose of this study was to investigate the gaps of bone-acetabular component interface, the initial mechanical stability and the effects of adjuvant screw fixation in the press-fitted two different shaped porous-coated acetabular components. Semi-hemispherical Harris-Galante II cup and full hemispherical Trilogy cup were press-fitted with or without adjuvant screw fixation in 40 bovine femur. The gaps of bone-implant interface were measured in each radiography of all specimen and axial compression tests and rotational stability tests were performed using servohydraulic tension-compression machine. There was significantly smaller gap at polar 1/3 region in the specimen implanted with Trilogy cup. But the adjuvant screw fixation did not affect the amount of gap. There was no significant statistical difference in axial load and rotational stability test in each situations of fixation. This study demonstrates that the initial mechanical stability is not influenced by the shape of semi-hemispherical Harris-Galante II cup and full hemispherical Trilogy cup and also independent of adjuvant screw fixation. But smaller gap of Trilogy cup at the polar 1/3 region indicates the possibility that less amout of wear debris of polyethylene or metal will be deposited and therefore less osteolysis or cup loosening will occur, but this hypothesis should be confirmed by the long-term clinical follow-up.