An optical imaging system includes a first lens including a negative refractive power and a convex object-side surface, and a second lens including a convex object-side surface and a convex image-side surface. The optical imaging system also includes a third lens including a negative refractive power and a convex object-side surface, a fourth lens including a convex image-side surface, a fifth lens, and a sixth lens including an inflection point formed on an image-side surface thereof. The first to sixth lenses are sequentially disposed in an optical-axis direction.