Pyridoxylated hemoglobin was modified with the activated ester of inulin. From the oxygen equilibrium curve, this conjugate was estimated to have about fivefold oxygen carrying capacity compared with a free hemoglobin. The half disappearance time of this conjugate in the circulation of a rat was 21 hours in contrast to 3 hours of a free hemoglobin. The oncotic pressure and the viscosity can be adjusted nearly equal to those of whole blood. This conjugate can be concluded to have sufficient properties for use as a blood substitute.