Background <p>Mental health inequalities exist across levels of neighbourhood socioeconomic disadvantage. Numerous reviews have examined the relationship between neighbourhood social, economic, and physical environmental attributes and mental health. However, reviews investigating whether environmental attributes present an opportunity to reduce neighbourhood socioeconomic inequalities in mental health are scarce. Therefore, the aim of the systematic review proposed in this protocol is to identify potential environmental moderators to neighbourhood socioeconomic inequalities in mental health.</p> Methods <p>The following electronic databases will be searched: PubMed, Scopus, Web of Science, PsycINFO, CINAHL Complete, GreenFILE and ProQuest. In addition, grey literature will be searched. Quantitative studies will be included if they include community-dwelling adults, with neighbourhood socioeconomic disadvantage as an exposure, mental health as an outcome and an objective measure of an environmental attribute as a potential moderator. Two reviewers will independently determine the eligibility of studies based on the inclusion/exclusion criteria. Data extraction and quality appraisal will be conducted. Data synthesis will be carried out and a&#xa0;meta-analysis will be considered if sufficient studies are available. If a meta-analysis is not feasible a descriptive summary of the study characteristics will be presented.</p> Discussion <p>Existing research illustrates the diversity of environmental attributes and the potential for them to moderate the association between neighbourhood socioeconomic disadvantage and mental health. Therefore, a synthesis of these studies is needed to inform urban planning policies aimed at reducing mental health inequalities.</p> Systematic review registration <p>PROSPERO registration number: CRD42024519354.</p>