In this study, a novel magnetically actuated robotic capsule (patent-filed, Alici and Zhou, 2019) is proposed for site-specific drug delivery inside the gastrointestinal tract. Retractable needles are equipped into the capsule-like robot to inject the drug directly into intended tissues, which will contribute to the full and fast absorption of the medication and consequently increase the efficacy of drug delivery. The needle is concealed inside the capsule initially and can be actively protruded and retracted by a magnetic membrane. A second magnetic membrane is employed to discharge the drug out of the reservoir and inject it into the targeted tissue through the needle. Besides active drug releasing, the robotic capsule is able to perform active locomotion controlled by an external magnet wirelessly. Theoretical and experimental analyses were conducted to characterize the magnetic membranes for the selections of these batteries-less soft actuators for wireless in-body drug injection. Both locomotion and drug injection tests were successfully performed with the prototypes inside the samples of the porcine small intestine, which validated the feasibility of the proposed drug delivery system.