Antigenic relationships between recent six serotype O field isolates of foot and mouth disease virus and the current used vaccine strain O1/3/93 can be rapidly determined sing one-way liquid-phae blocking sandwich ELISA. The most reliable  vaccine strain t control outbreaks caused by field isolates can be rapidly identified using the described relationship ‘r'. All virus isolates shared a closer antigenic relationship to the current used vaccine strain wit ‘r' values ranged between 0.8 and 1. A potent vacine containing the current used strain O1/3/93 could be the suitable vaccine to protect animals against existing serotype O field isolates.