Motivated by the presence of numerous dark matter clumps in the MilkyWay's halo as expected from the cold dark matter cosmological model,we conduct numerical simulations to examine the heating of the disk. Weconstruct an initial galaxy model in equilibrium, with a stable thin disk.The disk interacts with dark matter clumps forabout 5 Gyr. Three physical effects are examined: first the massspectrum of the dark matter clumps, second the initial thickness ofthe galactic disk, and third the spatial distribution ofthe clumps. We find that the massive end of the mass spectrumdetermines the amount of disk heating. Thicker disks suffer lessheating. There is a certain thickness at which the heating owing to theinteraction with the clumps saturates. We also find that theheating produced by the model which mimics the distribution found inStandard CDM cosmology is significant and too high to explain theobservational constraints. On the other hand, our model that corresponds tothe clump distribution in a ΛCDM cosmology produces no significantheating. This result suggests that the ΛCDM cosmology ispreferable with respect to the Standard CDM cosmology in explaining thethickness of the Milky Way.