The proposed paper discusses a new methodology to monitor the B-H curve of magnetic fluids, which have low relative permeability. The set-up consists of a magnetic circuit which encloses a sample. A first coil allows creating a magnetic field into the sample whereas a second one measures the flux density. A reluctance network taking into account the leakage flux is investigated in order to improve the result of a simple reluctance network. In fact, a comparison of the two reluctance networks is effectuated according to the Vibrating Sample Magnetometer measurement, which gives an error up to 80% for the simple reluctance network, while the relative error is equal to 20% with the new developed reluctance network presented in this paper.