A type of current transducer to the optical measurements of high-voltage current using ferrofluid films has been studied. The basic operation principle and design of the novel sensor is based upon the field-dependent transmitivity. When a thin film of ferrofluids is subjected to a magnetic field applied which is perdicular to the plane of film, a portion of magnetic particles is condensed out from the initially monodispersed magnetic fluid and forms magnetic chains, then the optical transmitivity of the ferrofluid changes. The main advantage of this method in comparison with the optical current transformer on Faraday effect and the conventional electromagnetic current transformer avoids problems in the low SNR and the high-voltage isolation. The sensitivity and response time can be tailored during fabrication to suit the application by changing the concentration, liquid carrier or changing the configuration of the transducer cell.