An optical imaging system includes: a first lens having positive refractive power, a second lens having negative refractive power, a third lens having negative refractive power, a fourth lens having refractive power, a fifth lens having refractive power, and an image sensor on an image side of the fifth lens such that the fifth lens is most adjacent to the image sensor. The first to fifth lenses are sequentially disposed from an object side to an image side of the optical imaging system and the optical imaging system includes a total of five lenses. The optical imaging system satisfies 1.3