OBJECTIVE: To determine if total calcium (Ca2+) intake and intake of Ca2+ from dairy sources are related to whole-body fat oxidation. DESIGN: Cross-sectional study. SUBJECTS: A total of 35 (21 m, 14 f) non-obese, healthy adults (mean ± s.d., age: 31 ± 6y; weight: 71.2 ± 12.3 kg; BMI: 23.7 ± 2.9 kg m-2; body fat: 21.4 ± 5.4%). MEASUREMENTS: Daily (24 h) energy expenditure (EE) and macronutrient oxidation using whole-room indirect calorimetry; habitual Ca2+ intake estimated from analysis of 4-day food records; acute Ca2+ intake estimated from measured food intake during a 24-h stay in a room calorimeter. RESULTS: Acute Ca2+ intake (mg·kcal-1) was positively correlated with fat oxidation over 24 h (r = 0.38, P= 0.03), during sleep (r = 0.36, P = 0.04), and during light physical activity (r = 0.32, P = 0.07). Acute Ca2+ intake was inversely correlated with 24-h respiratory quotient (RQ) (r= -0.36, P= 0.04) and RQ during sleep (r= -0.31, P= 0.07). After adjustment for fat mass, fat-free mass, energy balance, acute fat intake, and habitual fat intake, acute Ca2+ intake explained ∼10% of the variance in 24-h fat oxidation. Habitual Ca2+ intake was not significantly correlated to fat oxidation or RQ. Total Ca2+ intake and Ca2+ intake from dairy sources were similarly correlated with fat oxidation. In backwards stepwise models, total Ca2+ intake was a stronger predictor of 24 h fat oxidation than dairy Ca2+ intake. CONCLUSION: Higher acute Ca2+ intake is associated with higher rates of whole-body fat oxidation. These effects were apparent over 24 h, during sleep and, to a lesser extent, during light physical activity. Calcium intake from dairy sources was not a more important predictor of fat oxidation than total Ca2+ intake.