The paper introduces a semantic algorithm for building Industrial Symbiosis networks. Built around ontology modelling of knowledge in the domain of Industrial Symbiosis, the algorithm enables the acquisition of the explicit knowledge from the user through ontology instantiation and input/output matching based on semantic relevance between the participants. Formation of innovative Industrial Symbiosis networks is enabled by decomposition of properties characterising respective resources and solutions, the process optimised for set environmental criteria. The proposed algorithm is implemented as a web service. The potential of the algorithm is demonstrated by several case studies using real-life data. (C) 2015 Elsevier Ltd. All rights reserved.