The effect of oxygen partial pressure on viral replication was investigated with Vero/VSV system. At 10% oxygen partial pressure in spinner culture, VSV titer was significantly increased 130 fold compared to that obtained at 21%. A similar result was obtained for viral production in 1liter bioreactor. This implies that oxygen partial pressure during viral production has to be low. In low oxygen partial pressure, malondialdehyde concentration was decreased about 5 fold. Thus, low oxygen partial pressure allowed the reduced reactive oxygen species to be evolved, possibly by decreasing the random oxidation of the produced viral protein and membrane from the host cell.