BackgroundDecision aids (DAs) have been proposed to support patients and families with disease information processing and decision‐making, but their effectiveness for critically ill patients and their families is incompletely understood.AimTo systematically synthesize evidence on the effectiveness of the DAs on the prognosis of critically ill patients and knowledge, anxiety, depression and decisional conflict of their family members.Study DesignSystematic review and meta‐analysis. We conducted a systematic search of literature using PubMed, Embase, Cochrane Library, Web of Science, Cumulative Index to Nursing and Allied Health Literature database, Scopus, PsycNet, CNKI and Wanfang Database from the inception of the databases until May 2023 to identify randomized clinical trials (RCTs) describing DAs interventions targeted at adult intensive care unit (ICU) patients or their families. We also searched grey literature in four databases: Chinese Clinical Trials Registry, Chinese Cochrane Center, Open Grey and GreyNet International.ResultsSeven RCTs were included in the review. Meta‐analysis identified longer hospital length of stay (LOS) among all patients compared with usual care (mean difference [MD] = 5.64 days, 95% confidence interval, CI [0.29, 10.98], p = .04), but not in surviving patients (MD = 2.09 days, 95% CI [−3.70, 7.89], p = .48). However, there was no evidence of an effect of DAs on hospital mortality (RR = 1.25, 95% CI [0.92, 1.70], p = .15), ICU LOS (MD = 3.77 days, 95% CI [−0.17, 7.70], p = .06) and length of mechanical ventilation (MD = 0.88 days, 95% CI [−2.22, 3.97], p = .58). DAs led to a statistically significant improvement in family members' knowledge (standard mean difference = 0.84, 95% CI [0.12, 1.56], p = .02). We found no significant effect of DAs on anxiety, depression, post‐traumatic stress disorder, decisional conflict and quality of communication of family members.ConclusionsThis review provides effective evidence that DAs can potentially improve the knowledge level of family members while prolonging the hospital LOS among critically ill patients.Relevance to Clinical PracticeWell‐designed large‐scale studies with DAs tailored to the individuals' preferences and existing cultural values are warranted.