In current design practice, the thickness of the floor slab has been determined to satisfy requirement for deflection control. However, previous study shows that the floor thicknesses in residential buildings may not satisfy the floor vibration criteria, even though the thickness is determined by the serviceability requirements in current design provisons. Thus it is necessary to develop the procedure to determine slab thickness that satisfies the floor vibration criteria. This study attempts to propose slab thickness for flat plate slab systems that satisfies floor vibration criteria against occupant induced floor vibration(heel drop load). Two boundary conditions(simple and fixed support), three square flat plates(4, 6, 8m), and five concrete strength($18~30$ MPa) are considered. Since there are large uncertainties in loading and material properties, probabilistic approach is adopted using Monte-Carlo simulation procedures.