Aims and objectives: To evaluate the effectiveness of aromatherapy on agitation and aggression in patients with cognitive impairment. Background: The impact of aromatherapy on agitation and aggression has been evaluated in various studies, but there is uncertainty about their impact. Design: A meta-analysis of randomised controlled trials was undertaken. Methods: This meta-analysis was conducted under PRISMA guidelines. Following eight electronic literature databases were searched: Web of Science, PubMed, PsycINFO, Embase, Cochrane Library, Chinese Wanfang database, CNKI and VIP digital database from the inception of the databases up to 27 February 2021. Two reviewers assessed the risk of bias of the included studies independently using the Cochrane Collaboration tool. Overall, meta-analysis and three subgroup analyses regarding the type of aroma preparations, delivery mode and session length were performed using RevMan5.3 and stata14.0. Publication bias was assessed by visual inspection of the funnel plot asymmetry and Egger's regression test. Results: Fifteen studies comprising 693 participants were included. The meta-analysis indicated that aromatherapy could ameliorate agitation and aggression for cognitive impairment. The subgroup analysis based on the type of aroma preparations showed that lavender oil could significantly improve agitation and aggression. Most delivery modes of aromatherapy, including smearing and inhalation, were effective. Moreover, less length (≤4 weeks) aromatherapy showed a better effect on agitation behaviour than aromatherapy more than 4 weeks. Conclusions: Despite the meta-analysis indicating that aromatherapy could alleviate agitation and aggression especially short-term (≤4 weeks) aromatherapy inhalation in different conditions, further researches are needed to investigate the appropriate dosage of essential oils and the side effects. More well-designed randomised controlled trials containing participants from more countries are needed to verify our findings before we can make strong recommendations. Relevance to clinical practice: This meta-analysis suggested that aromatherapy should be considered as a complementary programme for patients with cognitive impairment patients. Medical workers could apply aromatherapy into daily routine cares for cognitive impairment patients.