D-003 is a mixture of higher aliphatic primary acids purified from sugar-cane (Saccharum officinarum L.) wax that inhibits platelet aggregation induced ex vivo by addition of agonists to platelet-rich plasma (PRP) of rats, guinea pigs, and healthy human volunteers. Because the ex vivo platelet aggregation model does not mimic properly platelet aggregation occurring inside the arteries, since all blood factors regulating the formation of a platelet aggregate or thrombus are not present in PRP, this work was undertaken in order to investigate the effects of different oral doses of D-003 on platelet aggregation induced by collagen in vivo in rats. Effects of single (5, 25, 100, and 200 mg/kg) or repeated doses (1, 5, 25, 100, and 200 mg/kg during 10 days) of D-003 on in vivo platelet aggregation in rats were studied. D-003 (5-200 mg/kg) orally administered as single or repeated doses inhibited significantly and dose-dependently collagen-induced platelet aggregation in rats. The minimal dose investigated effective in both single and repeated administration schemes was 5 mg/kg. The highest dose assessed in both cases was 200 mg/kg, causing inhibitions of 61.5% (single doses) and 74.4% (repeated doses). Thus, the effects of repeated doses were more pronounced than those obtained with single administration. The mean 50% effective dose of D-003 in both schemes was 2.3 mg/kg, which indicates a promising anti-thrombotic potential of D-003.