A safety syringe for taking blood has a hollow barrel having a bottom open end, a top end, a rectangular hole defined in the top end to have two opposite long sides and two opposite short sides, a needle hub detachably connected between the two opposite short sides of the rectangular hole and having a first needle extending from an elliptical body into an interior of the hollow barrel and a second needle extending away from the hollow barrel, a cap rotatably connected to the top end of the hollow barrel and having a notch defined through a periphery of the cap to receive therein the elliptical body so that the second needle extends out of the cap after in combination with the cap and an enclosure detachably enclosing the second needle for protection.