With the present worldwide direction for increasing the commitment of sustainable energy, the construction rate of wind farms is high, to achieve significant amount of the entire energy production. Energy production and consumption efficiency are the two main factors, that the location of a wind farm is dependent on them. There are many controlling parameters during selection a wind farm location such as; wind speed, possibility of connecting to the existing electrical networks, local population, and available construction site. Moreover, the choice of the optimal foundation system is an important aspect in the design of wind turbines. Suction buckets and monopiles are promising foundation options for offshore wind turbines, which are subjected to complex loading conditions resulted from both of self-weight of turbine and environmental loads including; wind, wave, and current. This paper aims to investigate the behavior of a monopile and a suction bucket as foundation proposals for offshore wind turbines. Comparative study are carried out between the two options under the same loading conditions using a three-dimensional finite element model by Plaxis3D software. The interaction between each foundation system and the subsoil is taken consideration during numerical analysis. The responses of a suction bucket and a monopile were analyzed and discussed. Therefore, interactions diagrams relating moment with lateral load (M-H) at different values of vertical loads (V) were presented. Also, the research was focused on initial lateral stiffness and initial rotational stiffness of the studied substructures. The effects of the related parameters on the response of the substructures in the two cases were discussed. Useful recommendations were revealed based on the obtained results.