AbstractParametric oscillations which occur in a nonlinear two‐phase circuit with nonlinear reactors and capacitors are applied to many kinds of power devices. When the devices are operating under light load, the output voltage of these devices exhibits unstable oscillations, i.e., subharmonic oscillations, quasi‐periodic oscillations or chaotic oscillations. This paper analyzes the abnormal oscillations and confirms the validity of the analysis experimentally.In this paper, new circuit equations are presented that can be applied to the analysis of a two‐phase nonlinear circuit in which reactor saturation curves are sharp. It is clarified by this analysis that the parametric oscillations of the circuit which contains reactors of moderate saturation characteristics become subharmonic or quasi‐periodic with the existence of resistances of the power supply side. Also, when the nonlinearity of the reactors in the circuit is sharp, the parametric oscillations may change into chaotic oscillations in addition to the aforementioned oscillations.