A lens adapter ring is provided for connecting a lens barrel to a lens holder whose thread specification is different from that of the lens barrel. The ring includes a first hollow cylinder. The cylinder includes a first inner surface and a first outer surface opposite to the first inner surface. The first outer surface includes a first outer thread portion adapted for the lens holder, and the first inner surface includes a first inner thread portion adapted for the lens barrel. The thread specification of the first outer thread portion is different from that of the inner thread portion. A lens module using the lens adapter ring is also provided.