In this paper, we focus on the effect of the non-Gaussian distribution in the fully-nonlinear wave on offshore platform response. The motion responses of two kinds of floating platforms are investigated numerically using a conventional time domain program. The input wave is generated using two methods. In the first method, linear wave components with randomly distributed wave phases are used as input in the time domain software as it is usually done in the global performance analysis during offshore projects. In the second method, the wave components come from a nonlinear irregular wave simulation using a potential numerical wave tank (PNWT). For both cases, twenty realizations of 3-hour duration are performed and the ocean wave is described by a JONSWAP spectrum. Then the response spectra, the probability distributions and the extreme responses of the platform motions and air gaps are compared.