An optical imaging system includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens. The first lens includes a negative refractive power, and the second lens includes a negative refractive power. The third lens includes a positive refractive power, and the fourth lens includes a positive refractive power, an object-side surface thereof being concave. The fifth lens includes a positive refractive power. The sixth lens includes a negative refractive power. The first to sixth lenses are sequentially disposed from an object side toward an imaging plane. One lens of the first to sixth lenses is cemented to a lens adjacent thereto.