Warm core is a typical structure of hurricanes and typhoons. It is a result of huge release of latent heat from the warm and moist inflow near the surface to form clouds and precipitation during the upward movement. The anomalistic high temperature to the ambient environment and the area of warm core correlate to the precipitation of hurricanes. The larger area and the higher temperature anomaly of the warm core is, the more precipitation from hurricanes is produced. This study uses the fourth channel of the Special Sensor Microwave Imager Sounder (SSMIS) onboard the U.S. Defense Meteorological Satellite Program (DMSP) F16 satellite to study the warm core of hurricanes Katrina and Rita which occurred in the fall of 2005. The channel is sensitive to the atmospheric layer between upper and middle troposphere and the brightness temperature from this channel reflects the effective layer temperature there. By investigating a time series of the satellite observations for hurricanes Katrina and Rita, we show that the warm core strengthens when the hurricanes reach maturity and that the warm core spreads and weakens after the landfall of the hurricanes.