Depression is a prevalent mental disorder in older adults, but the prevalence in older adults varies largely across studies due to differences in regional cultures and screening tools. The objective of this review is to systematically evaluate the global prevalence of depression in older adults. PubMed, Embase, Web of Science and Cochran Library databases were searched independently from 2000 to 2021. Subgroups, sensitivity, and meta-regression analyses were performed to address heterogeneity. Publication bias was evaluated using Egger's test. Forty-eight eligible studies were included in this review. The global prevalence of depression in older adults was 28.4%, with high between-study heterogeneity. The meta-analysis showed that the prevalence of depression in older adults is high although it varied with geographic regions, screening tools, sample sizes and representativeness, and study quality. Therefore, it is necessary to carefully consider appropriate screening tools to estimate the prevalence in different regions of a population.