A pulsed marginal oscillator has been developed for use in pulsed ion cyclotron resonance experiments. The circuit performs quite well as a means of detecting gaseous ions in a magnetic field when the cyclotron frequency of the ions is equal to the resonant frequency of the oscillator. A pulsed marginal oscillator is different from previous marginal oscillator designs in that a gated amplifier is incorporated in the feedback loop for pulsing the oscillator on and off. This feature is important for delayed detection of ions which are formed as a result of chemical reactions in the gas phase. Oscillation levels from 2 to 500 mV (p‐p) are obtained over a frequency range fram 50 kHz to 2 MHz.