Subunit vaccines containing haemagglutinin-neuraminidase (HN) glycoprotein of Newcastle disease virus (NDV), formulated as water-in-oil-in-water (W/O/W) emulsions, were prepared. First, the suitable constituents of a W/O/W emulsion adjuvant were investigated with polyvalent vaccines using NDV, infectious bronchitis virus and Haemophilus paragallinarum. The W/O/W emulsion adjuvant, composed of the antigen in phosphate-buffered saline (PBS), liquid paraffin, squalene, diglyceryl monooleate, polysorbate 80 and PBS in a 30:25:10:5:2:28 ratio, induced a good antibody response with less adverse local reactions. HN protein of NDV was expressed by an improved baculovirus expression vector, a hybrid nucleopolyhedrovirus (HyNPV) between Autographa californica NPV and Bombyx mori NPV,and was prepared from silkworm pupae infected with the recombinant baculovirus, HyNPV-HN. Then, the W/O/W emulsion vaccine containing HN protein was prepared using the aforementioned constituents. Chickens showed 100, 100 and 80% protection against challenge exposure to virulent NDV at 4 weeks after vaccination with W/O/W emulsion vaccines containing 30, 6 and 3% of HyHPV-HN-infected pupae, respectively. The vaccines containing HN protein did not induce adverse local reactions at the site of injection. The subunit vaccine for NDV containing HN protein expressed in the recombinant baculovirus-infected pupae, formulated as a W/O/W emulsion vaccine composed of the antigen in PBS, liquid paraffin, squalene, diglyceryl monooleate, polysorbate 80 and PBS in a 30:25:10:5:2:28 ratio, was therefore found to be safe and effective.