This work aims at developing a high sensitivity electronic oscillator, that shows a dependency between its oscillation frequency and the magnetic field. The proposed circuit is based on the Colpitts Oscillators topology, replacing the inductive element of the original configuration by a GMI (Giant Magnetoimpedance) sample. Such samples, under certain conditions, can be electrically modeled by inductances, that vary their values as a function of the magnetic field. The oscillation frequency of a Colpitts Oscillator is dependent of the inductance used in the circuit. Consequently, by using GMI sensor elements, this frequency will vary according to the magnetic field. In this way, it is possible to implement a transducer of magnetic field in frequency, which can be used to infer the magnetic field by measuring the oscillation frequency. In turn, the transducer sensitivity is enhanced by increasing the variation of the oscillation frequency in function of magnetic field variations. It is intended to use the circuit herein designed in ultra-weak magnetic field measurements, related to biomedical applications. The designed electronic circuit is presented and discussed throughout the text. The values specified for each component, on the theoretical design and on the experimental implementation, are highlighted and discussed. The designed theoretical circuit was compared to the assembled prototype and the observed discrepancies were presented and evaluated. It was developed a characterization system of the circuit with the purpose of optimizing its performance, aiming the maximization of its sensitivity and linearity, seeking at minimizing the harmonic distortions in the sinusoidal wave generated by the oscillator.