Objectives: Gratitude intervention, which requires participants to engage regularly in brief activities designed to cultivate a sense of gratefulness, is known as one of the most effective positive psychological interventions. Although numerous meta-analyses and systematic reviews have been conducted on gratitude intervention, no studies have focused on the working population. This study aimed to systematically summarize the effectiveness of gratitude interventions on workers' mental health and well-being. Methods: Systematic search was conducted in February 2021 using five databases. Eligible studies included randomized controlled trials implementing gratitude activities among healthy workers and measuring mental health or well-being indicators and original articles or thesis in English. Results: Nine out of 1957 articles met the inclusion criteria. Eight studies adopted gratitude list interventions, showing a significant improvement in perceived stress and depression; however, the effects on well-being were inconsistent. Interventions with gratitude list four times or less did not report significant changes in any outcomes. Conclusions: Most gratitude interventions incorporated a gratitude list, and some studies included gratitude activities as a part of the combined program. On the other hand, no studies focused on only behavioral gratitude expression among workers. Gratitude interventions might be effective in improving mental health, but their effects on well-being remain unclear. The total number of gratitude lists and reflections might influence the effect on mental health and well-being; however, due to the high heterogeneity of the studies, further studies are needed.