To provide a polyester resin for pressure-sensitive adhesives, which can give pressure-sensitive adhesive compositions excellent in adhesiveness to various adherends and excellent in adhesiveness to low polar adherends, such as polyolefins, especially without an adhesiveness-imparting agent such as a tackifier.

The polyester resin for the pressure-sensitive adhesives contains structures originated from a 18C fatty acid or a 18C fatty acid derivative as side chains. Also, a pressure-sensitive adhesive composition comprises the polyester resin for the pressure-sensitive adhesives, and a reactive compound capable of reacting with the polyester resin.