Injection of recombinant tissue plasminogen activator (rt-PA) is the standard drug treatment for thrombolysis. However, rt-PA shows risk of hemorrhages and limited efficiency even at high doses. Polysaccharide-poly(isobutylcyanoacrylate) nanoparticles functionalized with fucoidan and loaded with rt-PA were designed to accumulate on the thrombus. Fucoidan has a nanomolar affinity for the P-selectin expressed by activated platelets in the thrombus. Solid spherical fluorescent nanoparticles with a hydrodynamic diameter of 136 ± 4 nm were synthesized by redox radical emulsion polymerization. The clinical rt-PA formulation was successfully loaded by adsorption on aminated nanoparticles and able to be released in vitro. We validated the in vitro fibrinolytic activity and binding under flow to both recombinant P-selectin and activated platelet aggregates. The thrombolysis efficiency was demonstrated in a mouse model of venous thrombosis by monitoring the platelet density with intravital microscopy. This study supports the hypothesis that fucoidan-nanoparticles improve the rt-PA efficiency. This work establishes the proof-of-concept of fucoidan-based carriers for targeted thrombolysis.