Disclosed are a seat frame assembly and a method of manufacturing the same whereby adhesion of a reinforcing material attached to a seat frame is improved to secure rigidity of the seat frame and process speed is improved. According to one embodiment disclosed herein, seat frame assembly includes: a frame configured such that a portion of each of opposite sides is bent forward, and supporting an upper body of an occupant; and side members joined to the opposite sides of the frame, respectively, each of the side members including a groove formed in a surface being in close contact with the frame, wherein a portion of the frame that is surface-joined to each of the side members is provided with a protrusion inserted into the groove.