The mechanism of inducing convulsive seizure by Decadron was investigated as followings: 1) No convulsive seizure was observed after apllying Decadron solution at the motor area of cerebral cortex, but the typical convulsive was observed only by administrating it directly at Nucleus caudatus. 2) The convulsion induced by Decadron could be inhibited by Ca. Mg and homocarnosine. 3) Amongst sodium citratum like substances, citric acid, L-malic acid and oxalic acid were found to elicit the convulsion as Deeadron induced convulsion, but such as malonic acid, fumaric acid, maleic acid, α-ketoglutaric acid, succinic acid, oxalacetic acid and acetic acid were not. 4) Therefore, it was suggested that citric acid conbined in a non ion "complex" with Ca or Mg which inhibited irritability of the mortor neuron. And on the other hand, dexamethasone played the roll of an activator for inducing convulsion. These reactions in the brain are the most impotant factors for inducing the convulsive seizure.