High performance Cellulose Acetate (CA) ultrafiltration membranes were prepared by phase inversion technique using poly(ether-imide) (PEI) as the modification agent and Polyethylene Glycol (PEG-200) as pore former for hemodialysis. The morphology, hydrophilicity, water content, porosity, and ultrafiltration permeation rate of the prepared membranes were studied and were found to be improved significantly by the incorporation of PEI in the casting solution. The scanning electron microscopy (SEM) study indicated that, the incorporation of PEI increased the porosity and connectivity of pores between sub-layer and bottom layer in blend membranes. The water content, porosity, mechanical properties, and permeation rate of the membranes were increased considerably indicating the enhancement of hydrophilicity of the modified membranes. The biocompatibility of membranes was investigated through protein adsorption, platelet adhesion, and thrombus formation on the membrane surface. Anticoagulant activity of CA/PEI blend membranes was evaluated by measuring the activated partial thrombin time (APTT), prothrombin time (PT), thrombin time (TT), and fibrinogen time (FT). The results revealed that antithrombogenicity of CA/PEI blend membranes was increased significantly. Thus it is worth mentioning to note that, the highly biocompatible CA/PEI blend membranes prepared in this study would offer immense potential in hemodialysis.