Transitioning to renewable energy resources is necessary to address the energy and climate crisis and to be in accordance with UN Sustainable Development Goals (SDGs) 7, 11 and 13. Urban wind energy harvesting is still emerging mainly with the use of small wind turbines. Given their implementation challenges, positive and negative effects need to be weighed to make informed policy decisions and regulations. This systematic review evaluates the macro- and micro-scale environmental effects related to implementing small urban wind turbines (SUWTs). Although publications exist on diverse aspects of SUWTs, a review that addresses the broad range of identified environmental effects of SUWT implementations has been lacking until now. This review shows that while the study of the SUWTs’ environmental effects can build on the effects associated with large wind turbines, there are also significant differences. Given the heterogeneity of urban conditions, the implementation of SUWTs requires detailed local environmental assessment to characterise accurately most environmental effects, notably the net life-cycle primary energy performance and associated GHG emissions, raw materials depletion, recycling, safety, noise, visual and light pollution, and effects on urban wildlife. Effects that require further investigation and which possibly raise regulatory or social acceptance issues are identified and discussed. Policy relevance Harvesting urban wind energy can yield multiple environmental, efficiency and resilience benefits. However, several research and policy gaps remain to be addressed before deploying small wind turbines in urban contexts. These include: the need to quantify the net environmental gains of SUWTs based on their performance and life-cycle assessment; the structural implications of deploying SUWTs on existing buildings; the effect of SUWTs on local air quality and microclimates; the potential health and safety risks to those who may pass by; the effects of SUWTs on ecosystems; and the combined effects of SUWTs on people (e.g. noise or light annoyance). Further research and regulation can help to minimise the negative impacts and ensure social acceptability.