Results on the effect of Mo addition and thermal treatments on the magnetic properties of CoFeSiB in rotating water quenched amorphous wires are presented. It was found that the substitution of Co by Mo improves the wires glass-forming ability and thermal stability. The coercive field increases with about two orders of magnitude as compared to the value obtained in the as-cast state for the samples annealed at 550 degreesC, and the saturation magnetisation slightly decreases. The relative magnetic permeability first increases for temperatures at which the relaxation of the internal stresses induced during preparation process takes place and than decreases drastically. This behavior indicates a magnetic hardening of the samples.