Background We examined associations of objectively measured physical activity ( PA ) and sedentary time with cardiovascular disease biomarkers at age 60 to 64 years. This included investigation of sex differences and the extent to which associations may be mediated by adiposity. Methods and Results Participants were 795 men and 827 women aged 60 to 64 years from the Medical Research Council National Survey of Health and Development. Combined heart rate and movement sensors worn for 5 consecutive days were used to derive overall PA energy expenditure, kJ /kg per day) and time spent sedentary (<1.5 metabolic equivalent of tasks), in light PA (1.5-3 metabolic equivalent of tasks) and moderate-to-vigorous intensity PA (>3 metabolic equivalent of tasks). Linear regression models were used to relate each PA parameter to inflammatory (C-reactive protein, interleukin-6), endothelial (tissue-plasminogen activator, E-selectin) and adipokine (leptin, adiponectin) markers extracted from fasting blood samples. Greater time in light PA and moderate-to-vigorous intensity PA and less sedentary time were associated with more favorable biomarker levels. For C-reactive protein, interleukin-6, and leptin, these differences were greater among women than men. For example, % differences (95% confidence intervals) in leptin for men and women per SD increases in sedentary time: 7.9 (2.7, 13.0) and 20.6 (15.3, 25.8); light intensity PA : -3.8 (-8.9, 12.7) and -17.7 (-23.1, -12.4), moderate-to-vigorous intensity PA : -12.9 (-17.9, -8.0) and -18.3 (-23.4, -13.1). Fat mass mediated a greater proportion of these associations in women than men. Conclusions Greater light PA and moderate-to-vigorous intensity PA and less sedentary time in early old age were associated with more favorable cardiovascular biomarker profiles. Fat mass partially mediated these associations but more strongly in women than men, which explained sex differences.