Avian Influenza (AI) is a strategic communicable and zoonotic disease. The cause is a virus with Highly Pathogenic Avian Influenza (HPAI) subtype H5N1. The poultry market has important roles in the preservation, propagation, and spreads of the Avian Influenza (AI) virus from poultry to other species and humans. The purpose of this study was to determine the level of seroprevalence of Avian Influenza (H5N1) in free-range chickens at the Beringkit and Galiran market. A total of 120 free-range chickens were used as a sample. They have taken 60 serum samples per market. Serum removal is made from 5 merchants under the provisions of 3 samples from merchants who sell 6 to 10 free-range chickens. The sampling period is carried out for 2 months every 2 weeks 4 times. Sample testing was performed at the Denpasar Veterinary Centre with Haemagglutination (HA) and Haemagglutination Inhibition (HI) as barriers. The data titer of the antibodies obtained was analyzed by Non-Parametric Statistic Test Chi-Square (χ2) using IBM SPSS for windows. The results of the study showed that the AI subtype of the H5N1 subtype in both Beringkit Markets is 3.3% and Galiran Market is 6.7%, with seroprevalence in the two markets of 5.0% which is statistically not dissimilar (P<0.05). To prevent the transmissions of AI disease at the Beringkit Market and Galiran is recommended for vaccination and more attention to the market management and the free-range chicken maintenance system.