Polyethylene glycols (PEGs) are non-toxic, biodegradable and sustainable organic solvents, which find a large application in the chemical and pharmaceutical industry. In this study, we present the ring-closing metathesis reaction (RCM) in PEG under microwave irradiation. Several benchmark substrates, yielding 5- to 6-membered rings featuring di- or tri-substituted olefins, were evaluated. This study demonstrated that PEGs are suitable solvent for olefin metathesis. However, depending on the substrate/catalyst couple, isomerization may occur. (C) 2012 Elsevier Inc. All rights reserved.