The purpose of this study was to investigate the prevalence and epidemiological characteristics of late-onset hypogonadism (LOH) in middle-aged and elderly Chinese men. Two cross-sectional studies were conducted at 5-year intervals in community-dwelling men living in the same area. A total of 1472 (Study 1, S1) and 944 (Study 2, S2) men aged 40-69 years old were recruited as subjects. Subjects were evaluated through combining serum reproductive hormone levels with the Androgen Deficiency in Aging Males (ADAM) questionnaire and the Aging Males' Symptoms (AMS) scale. A significant difference was found in mean testosterone deficiency (TD) prevalence between S1 and S2, using either serum total testosterone (TT; 14.02% vs. 6.36%) or serum calculated free testosterone (cFT; 43.69% vs. 16.53%) cutoff values. According to the S1 or S2 data, the mean prevalence of LOH was 37.85%/15.47% in the positive ADAM test and 15.42%/9.43% in the positive AMS test (p < .01). According to classifications of TD based on gonadal status, the prevalence of secondary TD (27.34%) was higher than the primary (16.36%) and compensated (15.42%) TD in S1 (p < .01). However, there were significant differences among the prevalence of primary (6.89%), secondary (9.64%), and compensated (27.65%) TD in S2 (p < .05). Different types of testosterone levels, TD cutoff values, and questionnaires influenced the prevalence of TD and LOH. The serum FT cutoff value was an optimal threshold for evaluating and diagnosing TD and LOH, whose prevalence increased gradually with male aging.