Hemoglobin-loaded nano-sized particles with oxygen carrying capacity were prepared. All experiments were performed using biodegradable polymer poly (polyepsilon-caprolactone) (PCL) as matrix polymer. Optimized preparation parameters led to nanoparticles with well-defined characteristics such as size <200 nm, P50 27 mmHg and high encapsulation efficiency up to 99.4%. The results of in vitro and vivo studies suggested that Hb-loaded particles did not activate complements. After the nanoparticles suspension was injected into the mice via tail vein, the particles did not cause significant changes in total platelet counts. Apparently, the hemoglobin-loaded nanoparticles can serve as a potential candidate in substitution for red cells.