To compare the characteristics of body composition for different gender and age in a large number of apparently healthy Chinese subjects, and to determine reference values for fat-free mass index (FFMI) and fat mass index (FMI).In total, 61,382 Chinese adults (age range: 18-92 years) were consecutively enrolled into the study. Body composition was measured using bioelectrical impedance analysis with a tetrapolar impedance meter.The skeletal muscle mass, fat-free mass (FFM), FFMI and body mass index (BMI) were significantly higher in men than in women (P<0.05), but FM% and FMI were significantly higher in women (P<0.05). In the group with normal BMI (BMI 18.5-23.9 kg/m(2), 18-92 years), the reference values (5th-95th percentile) of FM%, FFMI and FMI were 9.7-34.5%, 14.15-19.76 and 1.99-7.75 kg/m(2) in men, and 18.1-35.8%, 13.82-17.89 and 3.68-8.16 kg/m(2) in women, respectively.Reference intervals for FFMI and FMI could be of practical value for the clinical evaluation of a deficit in FFM with or without excess FM for a given age category, complementing the classical concept of BMI in a more qualitative manner, although these indices are only suggestive indications for the degree of obesity. In contrast to BMI, similar reference ranges of FFMI seem to be more utilizable with advancing age.