There is provided a subminiature imaging optical system utilizing only three sheets of lenses having positive, negative and positive refractive powers, respectively. The subminiature imaging optical system comprising, sequentially from an object side: a first lens having a meniscus shape with a convex object-side surface, the first lens having at least one aspherical surface and positive refractive power; a second lens having a meniscus shape with a convex image-side surface, the second lens having at least one spherical surface and negative refractive power; and a third lens having both surfaces formed of an aspherical surface and having positive refractive power.