A subminiature imaging optical system including: a first lens having overall positive refractive power, the first lens including a first lens part having a convex object-side surface, a second lens part having an object-side surface in contact with an image-side surface of the first lens part and a third lens part having an object-side surface in contact with an image-side surface of the second lens part; and a second lens having overall positive refractive power, the second lens including a fourth lens part having an object-side surface with a convex center and a concave peripheral portion, about an optical axis, a fifth lens part having an object-side surface in contact with an image-side surface of the fourth lens part and a sixth lens part having an object-side surface in contact with an image-side surface of the fifth lens part, wherein the second lens part has a stop provided on the object-side or image-side surface thereof.