The present invention relates compounds of the formula A oligosaccharide-spacer-GpIIb/IIIa antagonist wherein the oligosaccharide is a negatively charged oligosaccharide residue comprising four to twenty five monosaccharide units, the charge being compensated by positively charged counterions, and wherein the oligosaccharide residue is derived from an oligosaccharide which has (AT-III mediated) anti-Xa activity per se; the spacer is a bond or an essentially pharmacologically inactive linking residue; the GpIIb/IIIa antagonist is a residue mimicking the RGD and/or K(QA)GD fragment of fibrinogen, typically comprising an optionally esterified carboxylate moiety and a basic moiety located within the residue at a distance of 10-20 ANGSTROM from each other; or a pharmaceutically acceptable saltthereof or a prodrug or a solvate thereof. The compounds of the invention have antithrombotic activity and can be used in treating or preventing thrombotic diseases.