Frailty is a common geriatric condition due to aging, defined as a decrease in the functional reserve to maintain the homeostasis. As part of the aging process, body composition changes occur. This study investigated the relationship between body composition and frailty in a community-dwelling elderly Korean population.This cross-sectional cohort study analyzed data of 2,385 elderly participants (aged 70-84 years, 1131 males and 1254 females) of the Korean Frailty and Aging Cohort Study from 2016 to 2017. Body composition, including total and trunk fat masses and fat-free mass, were measured with dual-energy X-ray absorptiometry. Fat mass index (FMI), trunk fat mass index, and fat-free mass index (FFMI) represented total fat mass, trunk fat mass, and fat-free mass according to height. Based on the frailty index developed by Fried, we compared the frail and non-frail groups. Poor physical performance assessed with the short physical performance battery score of < 9 is considered frailty. To evaluate the relationship between the variables, simple and fully adjusted multivariable logistic regression analyses were performed according to sex.Among the participants, 462 (19.3%) were defined as the frail group, with a significantly high mean age of 77.9 ± 4.0 years. In the logistic regression analysis of frailty based on body mass index (BMI) categories, underweight (BMI < 18 kg/m2) participants showed a high incidence of frailty in both sexes. BMI showed an association with frailty only in males. Lower FFMI was associated with a higher incidence of frailty in both sexes, which was statistically significant in the fully adjusted models. In the female, fat-related indexes including body fat percentage, FMI, and trunk fat mass index showed a significant association with poor physical performance. In contrast, males with low FFMI only showed a significant association with poor physical performance.Frailty was closely correlated with lower FFMI in both sexes. The poor physical performance associated with frailty correlated with fat-related body composition in females and fat-free mass in males, owing to the difference in body composition between the sexes. In the assessment of frailty, body composition and sex-related differences should be analyzed.