The fibrinogen receptor (integrin αIIbβ3), has attracted a considerable attention as a promising therapeutic target and its antagonists were applied for treatment of thrombotic disorders such as unstable angina, myocardial infarction, ischemic disease, atherosclerosis, and stroke. Herein, we report X-ray structure and antiaggregative properties of 6-(4-piperazinium-4-yl-benzoylamino)-2- (piperazin-1-ium)-4-oxo-3,4-dihydroquinazolin-1-ium chloride sulfate tetrahydrate (3). For the synthesis of 3, the following synthetic route was applied as outlined in Scheme 1. The single crystal X-ray analysis revealed that triclinic crystals, sp.gr. P-1 of 3 with unit cell a=7.782(1), b=11.959(1), c=15.807(2)Å, α=88.05(1), β=89.36(1), γ=78.14(1)°, V=1438.8(3)Å3 were obtained in the forms of chloride sulfate tetrahydrate. The target molecule is triply protonated on quinazoline and terminal nitrogen atoms on piperazine moieties. The latter are attached to phenyl and quinazoline moiety through equatorial and axial positions, respectively. The formula unit of 3 is shown on the figure. The organic cations are united in dimer via synthon, R22(8) NH…O(C=O) involving quinazoline moiety, and dimers further interact with anions and water molecules by charge-assisted and conventional hydrogen bonds. Functional activity was determined by measuring the inhibition of ADP induced platelet aggregation in human platelet-rich plasma by Born‘s method. The compound 3 inhibited platelet aggregation with IC50 of 1.3±0.1 μM. To define the mechanism of antiaggregatory action of compound 3, its influence on fluorescein isothiocyanate-labeled fibrinogen binding to integrin αIIbβ3 was studied on the suspension of washed human platelets. It was established that 3 had inhibited FITC-Fg binding to αIIbβ3 receptor in suspension of washed human platelets with IC50 value of 0.020±0.005 μM.