The removal of bacteriophage phiX174 and other viruses such as HIV and herpes virus was investigated by regenerated cellulose microporous hollow fiber membrane (BMM(R)) under the presence and absence of serum albumin or surfactants (i.e. Tween 80 and PEG400). The concentration of bacteriophage phiX174 in the solution, which has a mean diameter of 28 nm, was reduced to be less than 10(-8) times (i.e. logarithmic rejection coefficient, phi > 8) after the permeation through the membranes having mean pore size of 35 nm (BMM35) and 50 nm (BMM50), while the polio virus, which has approximately the same size as the bacteriophage phiX174, could not be rejected by the BMM35 and BMM50. The rejection of bacteriophage phiX174 decreased with an increase in additional concentration of the serum albumin or surfactants. However, the double step filtration of bacteriophage phiX174 by the BMM83 shows two times higher rejection than that of the single step filtration. Transmission electron microscopic observation of bacteriophage phiX174 on the BMM35 after its filtration showed the size of virus was confirmed to be 50-60 nm. With regard to the size of bacteriophage phiX174 (i.e. 28 nm diameter), the bacteriophage phiX174 was aggregated in the solution and the dispersion state of aggregated bacteriophage phiX174 is monodispersed from the result of the filtration of the BMM.