An optical imaging system is described including first to sixth lenses sequentially disposed from an object side to an image side, and an image sensor configured to convert incident light reflected from a subject, having passed through the first to sixth lenses, into an electrical signal. One of the first to sixth lenses includes a spherical object-side surface and another of the first to sixth lenses includes corresponding aspherical object-side surfaces. The first to sixth lenses include corresponding aspherical image-side surfaces, and a lens of the first to sixth lenses that is closer to the object side than the one of the first to sixth lenses including the spherical object-side surface, has a highest refractive index among the first to sixth lenses.