Hantaan virus (HTNV), strain Howang isolated from the blood of severe HFRS patient is a member of the genus Hantavirus family Bunyaviridae. The entire nucleoprotein (N) encoding S genome segment of the HTNV strain Howang was cloned and inserted into pRSET bacteria expression system and pBlueBac Baculovirus expression system ; and restriction enzyme digested partially overlapping S segments were inserted into pRSET bacteria expression system. These vectors allow the synthesis of a histidine-tagged fusion protein in E. coli and Baculovirus infected Sf9 cells. Expressed proteins were analyzed by western blot analysis using five nucleoprotein specific monoclonal antibodies derived against HTNV strain Howang. Three N monoclonal antibodies reacted to amino acids 35-65, one reacted to amino acids 244-290 and another one recognized conformational epitope. The monoclonal antibody that reacted to amino acids 244-290 ddid not crossreact to Seoul virus. These epitopes were analyzed by ELISA using synthetic peptides of 15 amino acids overlapping 5 amino acids derived above regions as antigen. The diagnostic value of the truncated N protein and synthetic peptides will be discussed.