Skin is an outermost organ that serves as an interface between the host and the environment. The skin provides not only mechanical barrier functions, but also an active immunological barrier that provides the first line of defense against infections. For the effective clearance of pathogens or antigens in the skin, immune cells must quickly exert their effector functions while avoiding the host damage by their excess activation. Therefore, the quality, magnitude, and the duration of the immune cell activity must be carefully regulated. Here, we will review our recent findings on the regulatory mechanisms for effector T cells activation in the skin, which was revealed by the live imaging techniques using two-photon microscopy.