In this paper the effect of magnetic field on the preparation of silver halide emulsion in gelatin by single jet method has been reported. The UV spectrum of magnetized AgNO3 solution showed the strength of absorption increased. SEM photographs and size distribution curves showed that silver halide grain obtained by magnetic treatment was more sizable and better-dispersed particles with longer diameter, compared with that without magnetic treatment. It has been confirmed that magnetic field does affect the crystallization process of silver halide in gelatin.