Fifteen rabbits were given a second degree scald on the back, then a large amount of fluid were given rapidly. In this way an acute diluted hyponatremia and a brain edema model were produced. In one group, the magnetotherapy was instituted immediately following the acut injury, while in the other group, it was started after the brain edema being developed. After giving a large quantity of fluid, the Na~+, CI~-, and K~+ concentrations in the blood were decreased and the quantity of water in the brain tissue was increased evidentely. The phenomena of neuron edema and widening of the perivascular space were also found. It was proved that the model of experimental brain edema could be produced on animals and the treatment and the prevention for brain edema could be obtained to advantage to certaiin degree. Also,it was better to use the magnetotherapy in brain edema as early as possidle.