An optical imaging system includes a first lens including a positive refractive power, a concave object-side surface, and a convex image-side surface. The optical imaging system also includes a second lens including a positive refractive power, a convex object-side surface, and a concave image-side surface. The optical imaging system further includes a third lens, a fourth lens, and a fifth lens. The first to fifth lenses are sequentially disposed from an object side to an image side.