<p>As a type of gray infrastructure that exists widely in cities, walls can provide habitats for a variety of species. To explore the ability of walls to increase biodiversity, we conducted a systematic literature review of articles evaluating the relationship between walls and urban biodiversity. We found that walls can improve urban biodiversity to some extent, but this enhancement may be limited by the characteristics and structural aspects of the walls themselves. Across the studies included in this review, there is a bias toward evaluating vascular plants and microorganisms, and most studies were carried out in developed countries. While the results of this study indicate that wall features are the primary factors that affect urban biodiversity, the narrow focus of the studies summarized in this study restricts our overall understanding of the relationship between walls and urban biodiversity. In the future, the planning and design of walls should be included in thematic discussions at the urban planning stage, and corresponding planning and design guidelines should be provided. The proportions and distribution patterns of different wall types, the distance and location relationships between walls and the surrounding land types, and other relevant factors should be comprehensively considered. Additionally, for walls with historical and cultural value, multiobjective planning strategies such as ecological balance, cultural protection and social development should be adopted to increase the ecological service function of the walls and improve the biodiversity of the city. By integrating biodiversity enhancement into wall design and management, cities can contribute to sustainable development goals (SDGs).</p>