Pieter Mertens (born 28 August 1980) is a Belgian former professional road bicycle racer. He competed as a professional for four years, riding for Vlaanderen–T Interim between 2004 and 2005 and for UCI ProTeam Davitamon–Lotto between 2006 and 2007. He announced his retirement in October 2007 in order to focus on his medical studies. His most notable victories include a stage of the 2005 Rheinland-Pfalz Rundfahrt and the overall title of the 2002 Tour de Namur. He competed in one Grand Tour: the 2006 Vuelta a España, finishing 75th overall.