This paper investigates the role of open innovation in the success of restaurants. Our research questions are as follows. 'Is open innovation a rational strategy for a small restaurant to attract and maintain customers? Which open innovation strategies should a small restaurant use?' We constructed our research model of open innovation ecosystem of restaurants with ingredients open innovation, recipe open innovation and service open innovation to analyse open innovation in small restaurants, which is a worldwide phenomenon. We chose four successful restaurants from Naples, one restaurant from South Korea, and a North Korean restaurant as our case studies using participant observation, in-depth interviews and semi-structured questionnaires, with the results indicating the following. First, open innovation is essential for the success of small restaurants. Second, if any small restaurant adopts a closed innovation strategy with respect to any of food ingredients, recipes or service, it should choose an open innovation strategy or open innovation platform with regard to the others to maintain its competitive advantage compared to other restaurants in the neighbourhood. Third, an open innovation platform of any of food ingredients, recipes or service, can generate additional revenue by selling independent ingredients or services.