This paper proposes a design method of low temperature co-fired ceramic(LTCC) diplexer, which is used to separate GPS and ISM band signals, achieves high iso lation and miniaturization, and can be used in electronic consumer products. The diplexer is composed of a low-pass filter and a band-pass filter. The antenna sep arates the received mixed signals according to frequency bands, and enters their respective processing modules through two output ports. The size of the diplexer is 1.6mm*0.8mm*0.6mm, the insertion loss is less than 0.6dB for GPS 1.575GHz appli cation, the isolation is greater than 26dB, and the insertion loss is less than 0.6dB for ISM 2.4/5GHz application, the isolation is greater than 37dB. Compared with the reported LTCC diplexer, the features of this diplexer are that the lower channel occupies a smaller volume at lower frequency, and the higher channel maintains low insertion loss in a wider bandwidth, and the passbands of the two filters are close but still have high isolation.