Two compact microwave band pass filters used in Ka band LTCC frequency synthesizer are presented in this paper. The filters are buried in the Ferro-A6 substrate. Modified SIR structure is employed to improve the stop band rejection and minimize the size of the LTCC BPF. The design processes are proposed. The measured results of the BPFs agree well with the simulation.Index Terms -LTCC, Ka band, band pass filter, frequency synthesizer.