High sensitivity, quick response, small size, non-contact sense and low-power requirement make amorphous wires attractive for sensor and micro-sensor realization. Influences of some negative factors accompany the operation of magneto-impedance sensors based on amorphous wires. They must be compensated for an efficient use of the devices and therefore the behaviour of the sensing element must be well characterized. The paper outlines the most important characteristics of amorphous wires and proposes an instrumentation set-up based on a vector analyzer for characterizing the behaviour of the sensors operating in real environment conditions.