A gear-forming cutter for forming a gear tooth on a non-metallic blank includes a spindle and a blade portion. The blade portion extends from the spindle along an axis of the spindle, and includes a blade surface and a surrounding surface. The blade surface has front and rear sides, and opposite first and second lateral sides. The surrounding surface is disposed around the axis, and extends from the first lateral side to the second lateral side. Any point of the first lateral side is spaced apart from the axis by a first radial distance. Any point of the second lateral side is spaced apart from the axis by a second radial distance smaller than the corresponding first radial distance. The first radial distance corresponding to the rear side is larger than that corresponding to the front side.