Objective: To observe the effect of amyloid fragment 25-35 (Aβ25-35) on ADP induced platelet aggregation and intracytoplasmic calcium of platelet for studing the action of amyloid on platelet. Methods: The venous blood of 18 healthy volunteers was adopted and determined the maximal aggregating rate of platelet (PAGmax) induced by adding different concentration of ADP in various level of Aβ25-35 (0, 5, 10, 20, 40 μmol/L). The basal concentration of ADP for affecting platelet aggregation by amyloid was defined as 1 μmol/L (EC50, the concentration of ADP for 50% maximal platelet aggregation). The alteration of intracytoplasmic Ca2+ ([Ca 2+]i) labelled by fluoresent calcium probe Fluo-3/AM was determined by different concentration of amyloid under confocal scanning microscope. Results: 1) Adding ADP into platelet rich plasma, the maximum of EC50 (26.33±6.57)% was obtained when concentration of ADP was 1 μmol/L, thus it was defined as the basal ADP concentration in determing the Aβ25-35 for affecting platelet aggregation. 2) The ADP induced PAGmax increased in different extent before and after the action of Aβ25-35. The maximal platelet aggregation rate was gradually increased as the increasing concentration of Aβ25-35 (P < 0.05). The highest platelet aggregation rate occurred in the group of 40 μmol/L Aβ25-35. The difference was significant (P < 0.01) compared with adding ADP only (0 μmol/L Aβ25-35). 3) The platelet intracytoplasmic [Ca2+]i concentration increased after inducing by Aβ25-35 and its increasing level was according to the concentration of Aβ25-35. The most significant increasing level of platelet [Ca2+]i (P < 0.01) established when existing 40 μmol/L Aβ25-35. Conclusion: The effect of higher concentration of Aβ25-35 may promote ADP induced platelet aggregation and increases platelet ([Ca2+]i) concentraion. It shows that the promoting effect of Aβ25-35 on platelet aggregation might be associated with the increasing level of platelet intracytoplasmic Ca2+ level.