Reactions of trimethylsiyldiethylamine, trimethylgermyldiethylamine, tri- methylstannyldiethylamime, and trimethylplumbyldiethylamine with pheny- lisocyanate were carried out at various temperatures for 4 days in sealed ampoules. In these all reactions, triphenylisocy an urate which is cyclictrimer of pheny- lisocyanate was mainly produced at low temperature, and diphenylcarbodi- imide was formed along with triphenylisocyanurate at high temperature, whereas, in the ease of trimethylsilydiethylamine, 1,3,5-tripheny 1-2, 4 6- tris (phenylimino) hexahydro-1,3,5-triazine and N, N’-diphenyluretidine-2,4- dione were given together with the compounds described above. The reactivity of group IVa Organometalamines for phenylisocynate were the fellowing order. Me₃pbNEt₂>Me₃SnNEt₂>Me₃GeNEt₂>Me₃SiNE₂ These group IVA organometalamines were only acted as catalysts.