A rip fence mechanism for being slidably connected to a worktable of a sawing machine includes parallel and spacedly arranged first and second rails, a fence plate pivotally connected between the first rail and the second rail in a way that the fence plate is pivotable between a vertical posture and a horizontal posture, and a support plate pivotally connected with the fence plate in a way that the support plate is pivotable between a first position where the support plate is abutted with the fence plate and a second position where the support plate is vertical to the fence plate. As a result, the lateral side of a to-be-cut workpiece can be directly stopped at the fence plate at the vertical posture and a bottom of the workpiece can be supported by the support plate at the second position during cutting.