Objective. Biological mechanisms mediating the effect of physical activity on the risk of coronary disease and stroke are not well established. We aimed to determine the effects of aerobic exercise and training on coagulation, platelet aggregation, and plasma lipids in healthy young adults. Methods. Sixteen subjects (mean age 26±4 years, 13 females) participated in a six-week low-impact, moderate-intensity aerobic exercise program. Platelet aggregation studies, Protime international normalized ratio (PT INR), activated partial thromboplastin time (apt), and plasma lipid determination were performed at baseline, after one exercise, after six weeks of training, and after two weeks of deconditioning. Results. After one session of exercise, mean platelet aggregation, aPTT, and PT INR did not change from baseline levels. After six weeks of training, however, we observed significant inhibition of ADP- and collagen-induced platelet aggregation in all participants (p≤0.0001) with prolongation of mean aPTT (p≤0.01) and PT INR (p≤0.0001). These effects persisted even after two weeks of deconditioning. Regardless of exercise, training or deconditioning, concentrations of total cholesterol, triglyceride, HDL-C, and LDL-C were not significantly different from baseline levels. Conclusions. Regular aerobic exercise elicited significant inhibition of ADP- and collagen-induced platelet aggregation as well as prolongation of PT INR and aPTT values, without significantly altering lipoproteins. The changes induced by training persisted even after two weeks of deconditioning.