The first Korean geostationary satellite Communication, Ocean, Meteorological Satellite (COMS) was launched on 27 June 2010 and is now located on 128.2oE. The onboard meteorological sensor measures IR brightness temperatures at three spectral bands centered at 3.7 um, 6.7 um, 10 um, and 12 um, and their calibration accuracies are of interest to assess. In this study, we try to examine the status of COMS IR channel calibration by intercomparing againt MODIS measurements at similar bands. However, since MODIS water vapor (WV) channel has 2-3 K bias compared to the IASI hyperspectral measurements, bias adjustment has been made before using the MODIS WV measurements as a reference. Assuming such bias depends on the season, theoretical relationship of relating MODIS measurements to COMS measurements is obtained on monthly basis, over a tropical region (30oN~10oS, 100oE ~160oE) in which satellite viewing angle (SVA) is smaller than 35o. Matched data were selected if time differences between two satellite measurements are within five minutes and their SVA difference is smaller than 5 degree. MODIS cloud mask results are used to select observations under the clear scenes. In January 2011, the COMS WV channel seems to have 1-2 K warm bias compared to the corrected MODIS WV channel measurements. The results of other three IR channels will be also shown in this investigation.