An optical imaging system includes a first lens having a negative refractive power, a convex object-side surface, and a concave image-side surface; a second lens having a positive refractive power; a third lens having a negative refractive power; a fourth lens having a positive refractive power; a fifth lens having a negative refractive power; and a sixth lens having a positive refractive power and an image-side surface having an inflection point. The first to sixth lenses are sequentially disposed in ascending numerical order from an object side of the optical imaging system toward an imaging plane of the optical imaging system.