To investigate serum antibody titers of Newcastle disease (ND) virus, serum samples were collected from 19,774 slaughtered chickens from 862 farms in Geoje, Goseong, Tongyung and other province during the period from January 2001 to December 2005. The results obtained are summarized as follows; 1. The negative percentage of ND antibody titer with below 1.0 levels decreased from 46.7% in 2001 to 40.5% in 2004 but those of it increased to 47.0% in 2005 and the positive percentage of ND antibody titer with higher 5 levels increased from 15.8% in 2001 to 26.2% in 2005. 2. The season levels of ND antibody titer showed various levels according to seasons but the general trend of ND antibody titer decreased in the later half of the year than those of the first half of the year. 3. The negative percentage of ND antibody titer on provinces decreased from 52.0% (2001) to 36.2% (2004) in Goseong but those of it increased to 51.4% in 2005. The negative percentage of ND antibody titer of Tongyung and other provinces increased from 51.0%, 28.5% (2001) to 55.0% and 44.3% (2005), respectively. 4. The year average levels of ND antibody titer increased from 2.2 to 2.6 during 2001- 2004 but those of it decreased to 2.4 in 2005. The provinces average levels of ND antibody titer increased from 2.0 to 2.8 during 2001 - 2005 and others provinces except Gyeongnam decreased from 3.3 to 2.6 during the 2001-2005. 5. The farm average levels of ND antibody titer with below 1.0 levels decreased from 26.3% in 2001 to 10.2% in 2004 but those of it increased to 17.6% in 2005 and those of below 1.0 or 2.0 levels increased from 17.9% (2001) to 27.7% (2005). The protective levels of ND antibody titer with higher 5.0 levels increased from 2.1% in 2001 to 8.8% in 2005.