Visibility was used as a long-term indicator of atmospheric haze caused by peat fires on the peat land area of the island of Sumatra, Indonesia. Visibility and the anomalies of sea surface temperature in the Ni¿o 3.4 region from 1973 to 2003 were analyzed. A significant linear relationship existed between the visibility and time, and the two signals shared two periodic components of 45 months (3.7 yr) and 61 months (5.1 yr), corresponding with the El Ni¿o-Southern Oscillation (ENSO) variability. Visibility decrease occurred about 3 months earlier than peak ENSO, suggesting fires initiated during the ENSO onset stage. The study demonstrated the connection of inter-annual climate variability, biomass burning, and air quality in the region. The study could facilitate the prediction of change in fire occurrence and air quality from ENSO monitoring data.