Background: Brown adipose tissue (BAT) dissipates heat and secretes anti- i nflammatory cytokines, known as BATkines, and is a potential strategy for promoting cardiometabolic health. A recent study demonstrated that BAT contributes to the utilization of certain serum amino acids (AAs), such as valine and leucine, which are known as branchedchain AAs (BCAAs), especially in subjects with high BAT following 2 hours of cold exposure. We hypothesized that the plasma AA profile would correlate with total hemoglobin concentration in the supraclavicular region (total-Hbsup) measured by near- i nfrared time-resolved spectroscopy (NIRtrs), and be a practical biomarker in the clinical setting. Therefore, in this study, we examined the relationship between the plasma AA profile under thermoneutral conditions (normal room temperature) and NIRTRS-determined BAT density (BAT-d) in a large-scale sample of both men and women. Methods: One hundred Seventy-three subjects (69 men, 104 women) aged 22-68 years were recruited during the winter season. AAs were comprehensively quantified using liquid chromatography-time-of-flight-mass spectrometry. The total-Hbsup, an indicator of BAT-d, was assessed using NIRtrs. Anthropometric parameters, including age, percentage of body fat, and visceral fat, were evaluated. Factors associated with higher (>74 pM) or lower (<74 pM) total-Hbsup were investigated by multiple logistic regression models that included AA concentrations alone (model 1) or AA concentrations and anthropometric parameters (model 2) as independent variables. Results: When adjusted for the false discovery rate, total-Hbsup was positively correlated with glycine and asparagine levels in men and with the serine level in both men and women and was negatively correlated with the branched-chain AA concentration in men. Models 1 and 2 correlated with higher or lower BAT-d for men (r = 0.73, P = 0.015) and women (r = 0.58, P = 0.079) and for men (r = 0.82, P = 0.0070) and women (r = 0.70, P = 0.020), respectively. Conclusions: A combination of anthropometric parameters and plasma AA concentrations could be a reliable biomarker for high and low BAT-d.