Despite the new opportunities created by digital technologies, today's participation processes in urban planning face major problems mainly regarding transparency, trust, and accountability. Therefore, the aim of the paper is to investigate how the implementation of blockchain technologies can impact the transparency of urban planning processes. Specifically, the study adopts an empirical approach through a case study analysis of an App BBBlockchain for citizen participation in urban planning decisions based on blockchain technology. From a preliminary investigation on the use cases called timestamping and document management, both addressing the first layer of participation which is information, the study draws some important conclusions on the positive and negative effects that blockchain has on transparency of urban development processes and repercussions on stakeholders' engagement. In particular, the findings suggest that blockchain alone cannot support transparency as conceived in this study as, there are some transparency dimensions which are beyond blockchain's influence.