$Stealth^{circledR}$ liposomes entrapped with streptokinase were prepared to improve the physical stability of conventional liposomes. The particle size distribution, dissolution rate and entrapping efficiency of the $Stealth^{circledR}$ liposomes were studied. The entrapping efficiency of streptokinase into conventional liposomes was proportional to the total lipid and cholesterol amounts. In $Stealth^{circledR}$ liposomes, the entrapping efficiency of streptokinase was increased with the increase of DPPE-PEG(5,000) amount. The particle size of $Stealth^{circledR}$ liposomes decreased with the increase of DPPE-PEG(5,000) amount. The dissolution rate of streptokinase from conventional liposomes was decreased by addition of cholesterol. The dissolution rate of streptokinase from the $Stealth^{circledR}$ liposomes was also decreased by addition of DPPE-PEG(5,000).