This paper presents the test results of Ka band qualification model multiplexers for Communication, Ocean and Meteorological Satellite (COMS) Payload to be launched in 2008. These are the input and output multiplexers of the satellite transponder to use available frequency resources effectively and the diplexer of the satellite antenna to use the same reflector for both transmitting and receiving frequency bands, respectively. The input multiplexer of the transponder with four frequency channels has four(4) independent channel filters which consist of a narrow 8-pole elliptic band-pass filter for high frequency selectivity and a 2-pole equalizer for group delay equalization. For low insertion loss, mass and volume reduction, manifold type is employed for output multiplexer. Dual mode technique is adopted in the cavities of channel filters for both input and output multiplexers for mass and volume reduction. The cavities are made of Invar with low thermal expansion coefficient that provides a stable RE performance over the specified temperature range and plated with silver to obtain the high unloaded quality factor. E-plane waveguide T-junction is used for either splitting or combining a frequency band into two sub-bands. Asymmetric inductive irises and capacitive irises are used to tune the receiving filter easily and to avoid the unwanted harmonic band for the transmitting filter, respectively. The electrical performance and environmental test such as vibration test, mechanical shock test, thermal vacuum test and EMC test are performed and the results of all qualification model multiplexers are compliant to the requirement of each multiplexer. Followed by this qualification, the flight model equipment will be developed for the COMS.