An apparatus for high pressure microwave experiments has been developed which can be operated at pressures up to 2 kilobars at 4.2 K using helium as the pressure transmitting medium. The high pressure chamber contains a rutile microwave resonator oscillating at ∼35 GHz. Microwave radiation is coupled into the resonator via a self‐sealing conical dielectric waveguide. The apparatus has been used in preliminary measurements of the effect of pressure on cyclotron resonance in bismuth.