In this paper, a compact 20 W block-up-converter for C-band satellite communication is designed and implemented. The designed block up-converter consists of an intermediate frequency circuit, a mixer and local oscillator, a driver amplifier, a solid-state power amplifier, waveguide circuits, and a power supply module. To reduce the size of the block-up-converter, all circuits are assembled within an housing, so its dimension is just $21{ imes}14{ imes}11cm^3$. Especially, the waveguide filter and microstirp-to-waveguide transition are easily implemented using an housing. Also, to meet spurious and harmonics specification, various compact microstrip filters including an elliptic filter are integrated. Measurement results show that the developed block up-converter has good electrical performances: the output power of 43.7 dBm, the minimum gain of 65 dB, the gain flatness of ${pm}1.84$, the IMD3 of -35 dBc, and the harmonic level of -105 dBc.