The present invention relates to a safety mechanism for microneedle injection, generally comprising an outer barrel unit and an inner barrel unit. The outer barrel unit includes an outer barrel body, a microneedle element, and a lid. The outer barrel body has an end that is a closed end and an opposite end that is an open end. The microneedle element is coupled to an outside surface of the closed end of the outer barrel body. The closed end of the outer barrel body is formed with one or more holes corresponding to the microneedle element. An inside surface of the closed end of the outer barrel body is provided with a tubular protruding post having a medication receiving chamber. The lid is assembled to the open end of the outer barrel body and formed thereon with a middle hole. The inner barrel unit comprises an inner barrel body, a piston, and a hollow needle structure. The inner barrel body has an end that is a closed end and an opposite end that is an open end. The piston is assembled at the closed end of the inner barrel body. The closed end of the inner barrel body and the piston are both formed thereon with holes that are coaxial and in communication with each other. The hollow needle structure penetratingly assembly in the inner barrel body. A front end of the inner barrel body is assembled into the tubular protruding post of the outer barrel body and an opposite end penetrates through the middle hole of the lid. The hollow needle structure includes a hollow needle, a support piece arranged at an end of the hollow needle, and push seat mounted to a middle section of the hollow needle. The push seat is formed with at least one annular groove. Moreover, the outer barrel body and the inner barrel body are each formed, to a side surface thereof, with an elongate slot penetrating therethrough and corresponding to each other. A push member having an end formed with at least one protrusion is inserted through the elongate slots of the outer barrel body and the inner
