An optical imaging system includes a first lens having an image-side surface that is concave; a second lens having a refractive power; a third lens having an object-side surface that is convex; a fourth lens having an image-side surface that is concave; a fifth lens having a refractive power; and a sixth lens having a refractive power and an image-side surface having an inflection point, wherein the first lens through the sixth lens are sequentially disposed in numerical order from an object side of the optical imaging system toward an imaging plane of the optical imaging system, and the optical imaging system satisfies TL/(2Y)≤1.01 and 1.2≤tan θ, where TL is a distance from an object-side surface of the first lens to the imaging plane, 2Y is a diagonal length of the imaging plane, and θ is half a field of view of the optical imaging system.