The accurate, consistent, and stable observations from different satellite missions are crucial for climate change detection. However, it is not an easy task to construct a consistent temperature record using measurements from different instruments in which the characteristics of the instrument may be changed due to its changing environment. The Global Positioning System (GPS) radio occultation (RO) can provide all-weather, high vertical resolution (from ~60 m near the surface to ~1.5 km at 40 km) measurements that have great potential for climate monitoring. Because the basis of the GPS RO measurement is a time measurement against absolute timed and calibrated atomic clocks on the ground, this data type is ideal for use as a climate benchmark. The six-satellite Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission was successfully launched in April 2006. With very high vertical resolution and accuracy, and about an order of magnitude of more soundings (~2500 profiles) than previously available, with uniform distribution in time and space, COSMIC presents a unique opportunity for comparing the vertical structure of atmospheric temperatures obtained from other satellite instruments. The objective of this study is to examine the usefulness of COSMIC RO data for climate monitoring. In this study, we use GPS RO data from the early phase of the COSMIC mission to compare Temperature in the Lower Stratosphere (TLS) taken from Advanced Microwave Sounding Unit (AMSU) microwave measurements from different satellites for potential improvements of stratospheric temperature trend analysis. We use COSMIC RO data to simulate microwave brightness temperatures, for comparison with AMSU Ch 9 measurements on board NOAA15, 16 and 18. Excellent correlation was found between synthetic COSMIC brightness temperatures (Tbs) and Tbs from NOAA15, NOAA16 and NOAA18, respectively. It is shown in this study that the synthetic COSMIC Tbs are very useful in identifying inter-satellite offsets among AMSU measurements from different satellites. To demonstrate the long-term stability of GPS RO data, we compare COSMIC dry temperature profiles to that from collocated CHAMP profiles. The fact that the mean CHAMP and COSMIC dry temperature difference between 500 mb to 10 mb can be as small as -0.021K provides strong evidence for the long-term stability of GPS RO signals. In order to assess the potential usage of the GPS RO calibrated AMSU Tbs to inter-calibrate other overlapping AMSU Tbs, we examine the uncertainty of the calibration coefficients derived from NOAA-GPS RO pairs. We found the difference between the COSMIC calibrated AMSU Tbs and that from CHAMP are in the range of ± 0.07 K with the standard deviation of 0.1K. This supports the robustness of the calibration coefficients found from NOAA-GPS RO pairs and demonstrates the potential to use the calibrated AMSU Tbs to calibrate other overlapping AMSU Tbs where no coincident GPS RO data are available.