The global effects of the 2004 El Niqo on tropospheric ozone and H2O based on Aura OMI and MLS measurements are analyzed. Although it was a weak El Niqo from a historical perspective, it produced significant changes in these parameters in tropical latitudes. Tropospheric ozone increased by 10--20% over most of the western Pacific region and decreased by about the same amount over the eastern Pacific region. H2O in the upper troposphere showed similar changes but with opposite sign. These zonal changes in tropospheric ozone and H2O are caused by the eastward shift in the Walker circulation in the tropical pacific region during El Niqo. During the 2004 El Niqo, biomass burning did not have a significant effect on the ozone budget in the troposphere, unlike the 1997 El Niqo. Zonally averaged tropospheric column ozone did not change significantly either globally or over tropical latitudes.