An optical lens system comprises, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, and a fourth lens element. The first lens element with positive refractive power has an object-side surface being convex in a paraxial region. The second lens element with refractive power has an image-side surface being convex in a paraxial region. The third lens element with positive refractive power has an aspheric object-side surface being concave in a paraxial region and an aspheric image-side surface being convex in a paraxial region. The fourth lens element with refractive power has an aspheric object-side surface being concave in a paraxial region and an aspheric image-side surface being convex in a paraxial region. There are a total of four lens elements with refractive power in the optical lens system.