This study is designed to probe for the effects of fat mass (FM) and fat free mass (FFM) on ventilatory function in adults. 1 307 healthy adults (372 males and 935 females) were selected from some localities of Heilongjiang province through random sampling by means of questionnaire and physical examination and measured for height, weight, waist to hip ratio (WHR), FM, FFM and ventilatory function. The data were analyzed by means of Pearson correlation analysis, independent-samples t test and multi-factors regression analysis. Regardless of sex, an independent positive correlation was found (P<0.001) between age and fat mass index (FMI). Regardless of sex, fat free mass index (FFMI) was found to be positively associated with forced vital capacity (FVC), forced expiratory volume in one second (FEV1), peak expiratory flow (PEF) and forced expiratory flow at 25% of forced vital capacity (FEF25%) (P<0.01), and FMI was significantly and negatively related to FVC, FEV1, FEF75% (P<0.05). In males FMI was significantly and negatively related to maximal mid-expiratory flow (MMEF) (P<0.05). Regardless of sex, the effect of FFMI on FVC was higher than that of FMI. For the males, the effect of FFMI on FVC was smaller than that of FMI, while the opposite was found in the females. Regardless of sex, FEF75% tended to decrease with increasing FMI, while FFMI was found to have no effects on FEF75%. MMEF tended to decrease with increasing FMI in the males, but no marked change was found in the females. The above results suggest that FM and FFM are independent factors influencing ventilatory function in adults. FM is negatively correlated with ventilatory function, but as a reflection of muscle mass, FFM is positively correlated with ventilatory function in adults. There is quantitative difference between the effects of FFM and FM on ventilatory function.