We report an electron spin resonance (ESR) study of the layered thin films of bathocuproine (BCP) and metal (Al or Au). Clear ESR signals with g = 2.0030 were observed for the samples containing Al owing to gap states at BCP/Al interfaces, while no ESR signal was observed for the samples containing Au. The ESR analysis shows that the spins are magnetically isolated with a maximum spin concentration of 1.7% per BCP monomer. The activation energy of spin motion is found to be very low, approximately 1 K, supporting the enhanced electrical conductivity in BCP layers with gap states. (C) 2014 Elsevier B. V. All rights reserved.