This systematic review aims to investigate and determine the effectiveness of interventions on improving mental health (anxiety, depression, stress or mental well‐being) and/or reducing burnout of nurses working in hospitals during the COVID‐19 pandemic. A search was conducted on studies from conception to December 2022 in databases: PubMed, Embase, Cochrane Central Register of Controlled Trials, CINAHL, PsycINFO, Scopus and Web of Science and in ProQuest Thesis & Dissertations Global Database, Google Scholar and ClinicalTrials.gov. A total of 17 randomised controlled trials that evaluated different interventions were included. The outcomes were anxiety (n = 11), depression (n = 5), stress (n = 13) mental well‐being (n = 7) and burnout (n = 7). Not all interventions led to positive outcomes. Grading of Recommendations Assessment, Development and Evaluation (GRADE) appraisal and risk of bias assessment using the Cochrane tool for randomised controlled trials (RoB 2.0) revealed poor quality of currently available literature, with low to very low certainty. Meta‐analysis showed high heterogeneity among the five different outcomes, with subgroup analysis showing greater success in interventions conducted on nurses involved in the care of COVID‐19 patients. More well‐designed trials are necessary to reinforce current evidence to improve the mental health of nurses, to not only protect their quality of life but also to ensure the quality of patient care.