Open innovation that is known as the use of purposive inflows and outflows of knowledge with a view to accelerate firms' own internal innovation, and expand the markets through external use of innovation is a very important window of opportunity for all firms to keep up with technology and survive. However, firms, which face lots of constraints to engage in open innovation, may be in tendency to closed approaches and reluctant to use open innovation. In terms of open innovation, however, our understanding of the factors, which are disincentives to apply open innovation, is still incomplete. On the other hand, science and technology parks are the platforms that enable firms to innovate in an open system thanks to their networking nature across universities, research labs, start-ups, SMEs, and large firms. In this context, this study aims to explore the factors that obstruct the use of open innovation based on the data gathered from 102 ICT firms that operate in science and technology parks in Turkey. Constraints to open innovation that are compiled from relevant literature are subjected to exploratory factor analysis to reduce the number of variables, and uncover some new structures. Constraints concerning "confidentiality and conservativeness of the firm", "human resources, brand and image", "resources and costs", "management and organization", "market, partnership, and technology sources" and "administration" are found as the constraints to open innovation faced by firms operating in science and technology parks. (C) 2016 The Authors. Published by Elsevier Ltd.