Abstract: A C-band magnetically insulated transmission line oscillator (MILO) has been designed, manufactured and tested. The C-band MILO typically operates in single-shot mode with 437~464 kV, 36~39 kA beam pulses, generating 1.60~1.68 GW high power microwave pulses at 3.60~3.66 GHz. The output powers radiate through the extractor coax, where they propagate in the TEM mode. The power conversion efficiency is greater than 9% in experiments. The experimental results agree well with the simulations.