Objective:To compare the prevalence of frailty and related factors in middle-aged and elderly people aged ≥45 years in island and mountainous areas of Taizhou, Zhejiang Province.Methods:Based on cross-sectional design, stratified cluster sampling and quota sampling methods were adopted. One administrative district was randomly selected from each of six coastal and three inland administrative districts in Taizhou during July to August, representing two different geographical terrains. In the island area (Jiaojiang District), all residents aged ≥45 years were included by cluster sampling. In the mountainous area (Xianju County), participants were selected through quota sampling, with same gender and age distributions. Data about their demographic characteristics, lifestyle and health-related factors were collected through questionnaire surveys and laboratory examinations. The prevalence of frailty was assessed using the Fried frailty phenotype scale. Hierarchical analysis and multivariate logistic regression analysis were used to compare the influencing factors of frailty.Results:A total of 1 011 local residents were studied, in whom island and mountainous residents accounted for 48.1% (486/1 011) and 51.9% (525/1 011) respectively; men and women accounted for 45.9% (464/1 011) and 54.1% (547/1 011) respectively. Middle-aged (45-49 years), younger elderly (60-74 years), and older elderly (≥75 years) residents accounted for 38.6% (390/1 011), 44.6% (451/1 011), and 16.8% (170/1 011) respectively. The overall prevalence rate of frailty was 3.6% (36/1 011), the prevalence rate was 3.7% (17/464) in men and 3.5% (19/547) in women. The prevalence rates in age groups 45-59,60-74 years and ≥75 years were 0.3% (1/390), 2.2% (10/451), and 14.7% (25/170), respectively. The prevalence rates of frailty and pre-frailty in island area were 6.0% (29/486) and 39.1% (190/486), respectively, which was higher than those in mountainous area (1.3%, 7/525) and (30.9%, 162/525). After adjusting for potential confounding factors, the risk for frailty in island residents was significantly higher than that in mountainous residents (a OR=1.55,95% CI: 1.07-2.25, P=0.019). In island area, older age (60-74 years:a OR=2.52,95% CI: 1.56-4.13; ≥75 years:a OR=11.65,95% CI:5.38-26.70), being women (a OR=1.94,95% CI: 1.20-3.17), suffering from depression (a OR=1.09,95% CI:1.02-1.17) were associated with frailty symptoms. In mountainous area, older age was also associated with an increased risk of frailty symptoms, but the OR value was lower than those in island area (60-74 years: a OR=1.74,95% CI:1.04-2.94;≥75 years: a OR=4.78,95% CI:2.45-9.50). Polydrug use (a OR=2.08,95% CI: 1.14-3.80) and suffering from depression (a OR=1.10,95% CI: 1.02-1.18) had significant positive association with frailty symptoms. Higher education level had significant negative association with frailty symptoms (junior high school: a OR=0.40,95% CI: 0.21-0.75; senior high school and technical secondary school: a OR=0.29,95% CI: 0.15-0.53; college or above:a OR=0.22,95% CI: 0.11-0.42). Conclusions:The prevalence of frailty in middle-aged and elderly community residents was significantly higher in island area than in mountainous area in Taizhou. The frailty-related factors varied with area. The elderly people (≥75 years) and women in island area had higher risk for frailty. Older age and suffering from depression were the independent risk factors for frailty. It is necessary to pay attention to the health risk factors and special environment in island area, and take comprehensive intervention measures to delay the process of debilitation and improve the quality of life of middle-aged and elderly people.