Background: Weight loss is a common phenomenon among the elderly and is identified as an important indicator of health status. Many epidemiology studies have investigated the associa-tion between weight loss and dementia, but the results were inconsistent. Objective: To examine and determine the association between weight loss and the risk of dementia. Methods: Eligible cohort studies involving weight loss and dementia were searched from PubMed, Embase, and Ovid databases through October 2018. Pooled relative risks (RRs) with its 95% confi-dence intervals (CIs) were used to estimate the effects of weight loss on the risk of dementia. Sub -group and sensitivity analyses were performed to explore the potential sources of heterogeneity. The Begg's test and Egger's test were used to assess the publication bias. Results: A total of 20 cohort studies with 38,141 participants were included in this meta-analysis. Weight loss was significantly associated with the risk of dementia (RR=1.26, 95% CI=1.15-1.38). BMI decline >= 0.8 units (RR=1.31, 95% CI=1.10-1.56) and >= 4% (RR=1.19, 95% CI=1.03-1.38) could increase the risk of dementia. The risk of all-cause dementia for people with weight loss in-creased by 31% (RR=1.31, 95% CI=1.15-1.49), and 25% higher for incident Alzheimer's disease (RR=1.25, 95% CI=1.07-1.46). Weight loss in participants with normal weight had a similar de-mentia risk (RR=1.21, 95% CI=1.06-1.38) with the overweight individuals (RR=1.22, 95% CI=1.11-1.34). Conclusion: Weight loss may be associated with an increased risk of dementia, especially for Alzheimer's disease. Maintaining weight stability may help prevent dementia.