OBJECTIVE: To evaluate the effect of low-dose aspirin on the deposition of platelet at the anastomotic site and the function of coagulation system in order to provide experimental data for clinical use. METHODS: (1) Twenty-eight SD rats were divided into experimental group (n = 21) and control group (n = 7), aspirin were administered through a catheter placed in the femoral vein in dose of 4 mg/kg in the experimental group and the same dose of normal saline in the control group. The experimental group was subdivided into 3 groups, with 7 rats in each group, according to survival time of 24, 48 and 72 hours after dose. Samples of 4 ml blood were taken by heart puncture from each rat to investigate the maximal platelet aggregation rate(MAR), prothrombin time(PT) and kaolin partial thromboplastin time(KPTT). (2) Sixteen New Zealand White rabbits were divided into experimental and control group, 8 rabbits in each group. Drugs were given in the same way. Forty-eight hours later, the bilateral femoral arteries of each rabbit were exposed and arteries between inguinal ligament and the origin of the superficial epigastric arteries were transected and end-to-end anastomosis was completed with interrupted suturing technique. Fifteen and 120 minutes after the recovery of blood flow, the left and the right vessels containing anastomotic sites were harvested respectively and treated with 125I-labeled anti-GP IIb/III a antibody (SZ-21) using radioimmunobinding method. The radioactivities of the anastomosed vessels were measured. RESULTS: The KPTT in the experimental group was longer than that of the control group at 24- and 48-hour group, the mean percentages of increase were 42.56% and 35.33% respectively, and there were very significant differences between the experimental and control group in 24-hour group (P lt; 0.001). The PT value in experimental group was longer than that of the control group, but there was no significant difference (P gt; 0.05), and the maximal aggregation rate of platelet in the experimental group was significantly lower than that of the control group after 72 hours (P lt; 0.001). The radioactivity of the anastomosed arteries in the experimental group were significantly higher than that of the control group (P lt; 0.001) at 15 minutes after the recovery of blood flow, the mean percentage of increase was 110%. CONCLUSION: Low-dose aspirin can significantly affect the function of the intrinsic coagulation system, prevent the aggregation of platelets, but no effect on the function of the extrinsic coagulation system. On the other hand, it can also increase the deposition of platelet on the anastomotic sites after end-to-end anastomosis, especially in the early stage when it is intravenously injected, but it is b enough to cause thrombosis at the anastomotic sites. The effects of low dose aspirin on the coagulation system are inconsistent with its local effects on anastomotic sites.