Quantum state transferring has been demonstrated using drones via entanglement distribution. Here, we demonstrate the first drone-based quantum task for quantum key distribution (QKD). Compact and polarization-maintaining acquisition, pointing, and tracking systems and QKD modules are developed and loaded on a homemade octocopter with a takeoff weight of 30 kg. Real-time QKD is performed over a 200 m distance with an 8.48 kHz average secret key rate using a polarization-coded decoy-state BB84 protocol. With the capability of secret key distribution using a drone, wireless communication can be expected with enhanced security in the quantum approach between mobile nodes toward a network.