Lightning Protection System (LPS) must be properly designed to guarantee safe levels of transient voltages for people in the surrounding of the hit building and avoid damage to equipment. LPS comprises an upper grid, down conductors, and a grounding system (GS) in this context. The latter comprises an arrangement of vertical and horizontal electrodes whose precise representation must consider the frequency-dependent impedance and that these conductors are buried into a frequency-dependent soil. Additionally, the upper grid and down conductor can be represented by many transmission line models available. This paper investigates transient currents and voltages for an LPS subjected to lightning strikes, whose grounding system is buried in homogeneous frequency-constant (FC) and frequency-dependent (FD) soils. Results show that transient responses are considerably affected by the frequency dependence of the soil parameters, which are more pronounced in soils of high resistivity.