We observed with a confocal scanning laser microscope the interface between a liquid crystalline polymer (LCP) and polydimethylsiloxane (DMS) after they made contact. The initially flat interface became corrugated and the characteristic length of the corrugation increased gradually. The coarsening rate was found to be controlled by the viscosity (the molecular weight) of the DMS; as the viscosity was increased the rate became slower. The present interfacial instability may be related to the diffusion of the low molecular weight DMS into the LCP. (C) 2003 Elsevier Ltd. All rights reserved.