An optical imaging system includes first through seventh lenses. The first lens includes positive refractive power, the second lens includes a positive refractive power, the third lens includes a negative refractive power, an object-side surface thereof being convex, the fourth lens includes a positive refractive power, the fifth lens includes a negative refractive power, the sixth lens includes a negative refractive power, and the seventh lens includes a negative refractive power and having an inflection point formed on an image-side surface thereof. The first to seventh lenses are sequentially disposed from an object side toward an imaging plane.