A method for preparing a metal catalyst supported on a porous carbon support using a plant, including: (a) a step of preparing a plant; (b) a step of preparing a metal precursor-absorbed plant by absorbing a metal precursor into the plant; (c) a step of preparing a catalyst precursor by drying the metal precursor-absorbed plant; (d) a step of preparing a char by charring the catalyst precursor; and (e) a step of preparing a metal catalyst supported on a porous carbon support by treating the char with an acid. The method for preparing a metal catalyst supported on a porous carbon support of the present disclosure, whereby a plant itself is charred, is environment-friendly and allows for convenient large-scale synthesis. The metal catalyst supported on a porous carbon support prepared thereby can be used as electrode materials of various energy devices, particularly as an electrode catalyst of a fuel cell.