Challenges for a sustainable urban development are increasingly important in cities because urbanization and related land take come up with negative challenges for the environment and for city residents. Searching for successful solutions to environmental problems requires combined efforts of different scientific disciplines and an active dialogue between stakeholders from policy and society. In this paper, we present a comparative assessment of the way policy-science dialogues have achieved knowledge co-production about strategic urban environmental governance action using the cities of Berlin in Germany and Rotterdam in the Netherlands as case studies. The ecosystem services framework is applied as a lens for policy-science interaction and a 'knowledge co-production operating space' is introduced. We show how policy officers, urban planners, practitioners and scientists learned from each other, and highlight the impact of this knowledge co-production for governance practice. We found that the concerted collaboration and co-creation between researchers and policy officers have led to mutual learning and establishment of relationships and trust in both cities. Not only the policy-relevance of research and its policy uptake were achieved but also new insights for research blind spots were created. In our conclusions we reflect on co-production processes with two types of conditions that we introduced to be most influential in the way knowledge can be co-created. These are conditions that relate to the way knowledge co-production processes are set-up and, conditions that relate to the expected value or benefit that the co-produced knowledge will bring across society, policy and practice.