The integration proposed by the microgrid is especially addressed to those types of resources that can be defined as renewables energy resources. Due to the decarbonization process that is involving many sectors, among which, the mobility sector, electric vehicles (EVs) can be considered a challenging way to less pollute the environment, and at the same time, they can be viewed as mobile energy storage systems. This paper considers an islanded microgrid (MG) structure, where, in addition to the presence of energy conversion from renewable and fossil sources, the connection of EV is envisaged. Their presence makes it possible to take advantage of vehicle-to-grid (V2G) technology for the frequency regulation service. The MG system is simulated in a MATLAB / Simulink environment and, considering a day of variable time, four case studies are carried out, varying the number of EVs connected to the system. The results of the simulations show how EVs provide a valid aid to frequency regulation, given their rapid response, in terms of injection or absorption, to variations in the power fed into the MG from renewable sources. However, the number of EVs connected to the MG must be sized according to the powers involved; an excessive number of vehicles available for regulation does not always benefit the system.