The feasibility of fractionation of the water-soluble chitooligosaccharides prepared with the nitrous acid degradation of chitosan was evaluated. A modified clotting time assay and the platelet coagulation test were carried out to determine their preliminary blood compatibility. The water-soluble portion of the fractionated products was also characterized. Using a turbidimetric aggregation monitoring device, the platelet coagulation was measured. It was found that the coagulation time of the 10 wt.% chitooligosaccharides solution was prolonged as compared with (PBS).