The micromechanical systems include devices and technology such as actuators and electronic elements on a micrometric scale.A key piece for the development of these systems are the micro cantilevers, which mechanical and dynamic features allow to design sensors and actuators, among others.However, the dynamic response of a microcantilever is altered when it is immersed in a fluid, such as water or even air.Thus, the physical models that describe their behavior in normal conditions (vacuum) do not apply.Considering this condition, this article presents the physical models that describe the behavior of the microcantilevers in fluids (water and air) through the analysis by finite elements.The results show that the density and viscosity of the fluid alter both the oscillation amplitude of the microcantilever and modify the oscillation frequency.Nevertheless, the behavior of the microcantilever in vacuum and air are approximate.