An optical imaging system includes, in order from an object side to an image side: a first lens element having positive refractive power, a second lens element having negative refractive power, a third lens element, a fourth lens element, a fifth lens element having both an object-side surface and an image-side surface being aspheric, and a sixth lens element having both an object-side surface and an image-side surface being aspheric, wherein the optical imaging system has a total of six lens elements; at least one lens element among the first lens element, the second lens element, the third lens element, the fourth lens element, the fifth lens element, and the sixth lens element has at least one inflection point.