In the past, osteoporosis is usually viewed as a woman disease. However, men and women are shown to lose their bone mass at the same rate by more than 65 of age, and osteoporosis in men causes higher mortality in men than those in women. Thus, osteoporosis in men has recently aroused public attention. Androgen deficiency was the main cause leading to osteoporosis. Bone structure is maintained by a dynamic balance of osteoblast-mediated bone formation and osteoclast-mediated bone resorption. Androgens and androgen receptor (AR) play critical roles in regulation of bone formation and resorption. MicroRNAs (miRNAs) are non-coding small RNAs and participate in regulating activities of osteoblasts and osteoclasts by postranslationally targeting certain gene expressions. miR-133 and -135 can target BMP-2, Runx2, and Smad5 and then regulate osteoblast differentiation. Likewise, miR-141 and -200a negatively regulated osteoblast differentiation. Nevertheless, the functional roles of miRNAs in osteoporosis in men are still unknown. In addition, miRNA are stable and can be detected in the blood as novel biomarkers for certain diseases. A recent study analyzed the levels of miRNAs in circulating monocytes of 10 high and 10 low bone mineral density postmenopausal Caucasian women and found miR-133a is a potential biomarker for postmenopausal osteoporosis. In comparison, the roles of blood miRNAs in osteoporosis in men have not been evaluated. Therefore, this study is aimed to evaluate the roles of specific miRNAs in osteoporosis in men.