Equine influenza disease is attended by inflammation in upper respiratory tract and a common disease in horse. This study was conducted on horses in Tabriz area in Iran for seroprevalence of this disease. Blood samples were taken from 192 horses (166 males and 26 females). On the bases of age these cases were divided in 5 groups (6 months - 2 years (4 samples), 2-4 years (22 samples), 4-6 years (42 samples), 6-8 years (50 samples) and over 8 years (74 samples). Serum samples were transmitted to Laboratory and then seroprevalence was investigated by ELISA method (IDVET kit). In 14 horses (7.3%) was positive, in 4 horses (2.1%) was doubtful and in 174 horses (90.6%) was negative. Mean positive percent (pp) of equine influenza virus in positive samples, 22.29 ± 2.57, in doubtful samples 45.50±0.29 and in negative samples 87.07± 0.97 was recorded. It is determined that there is no significance difference between males and females in term of seroprevalence of this virus, although mean positive percent in males was less than females. Maximum mean positive percent was in 6 months - 2 years of age group, and minimum was in above 8 years of age, difference between mean among age groups was significance (p<0.05). It is concluded that there is serologic infection of equine influenza virus in Tabriz area, it seem quarantine acts and horses trading control is necessary and use of vaccination is advised to ranchers.
