Plant cells express a target protein, a production method thereof, and a method of producing a target protein using the same are disclosed. The plant cells have introduced therein a recombinant vector containing gene(s) encoding a target protein, and the plant cells include plant cambial meristematic cells (CMC) or callus. The cambial meristematic cells (CMCs) are a cell line containing innately undifferentiated cells isolated from a plant, wherein the cell line is a cell line isolated from the cambial tissue of the plant and has meristematic continuity without going through dedifferentiation into callus. A system of expressing a target protein using the recombinant plant cells according to the present invention can overcome the problems of conventional plant cell culture. In addition, it shows significantly high transformation efficiency, and thus can produce large amounts of target proteins, including biopharmaceutical proteins.