In this paper, the compact size and low profile integration passive device (IPD) diplexer is designed based on IPD process. The overall size of IPD diplexer is 1.0mm by 0.5mm with thickness less than 0.3mm with solder ball. Through electromagnetic (EM) solver, the insertion loss on low-band and high-band is below 1dB and better than LTCC solution. In addition, its attenuation is excellent compared to LTCC component. In real applications, a wireless system-in-package (SiP) module is designed by using the IPD diplexer. The simulated insertion loss of low and high channels not only shows better electrical performance, but also has a more compact size than LTCC solution.