An optical imaging system includes a first lens having a positive refractive power, a second lens having a refractive index of 1.65 or greater, a third lens having positive refractive power and a refractive index of 1.65 or greater, a fourth lens having a positive refractive power, a fifth lens having a refractive index of 1.65 or greater, a sixth lens having a refractive index of 1.65 or greater, and a seventh lens having a positive refractive power. The first to seventh lenses are sequentially disposed from an object side to an imaging plane.