An optical imaging system includes, in order from an object side to an image side, a first lens element with positive refractive power, a second lens element, a third lens element, a fourth lens element, and a fifth lens element. Each of the fourth lens element and the fifth lens element includes at least one aspheric surface. The fourth lens element and the fifth lens element are made of plastic. The fifth lens element includes a concave image-side surface and at least one inflection point. An axial distance is formed between each of the first lens element, the second lens element, the third lens element, the fourth lens element, and the fifth lens element, and the optical imaging system further comprises a stop.