Reactions of triethylstannyldiphenylphosphine with phenylisocyanate were carried out at various temperatures in sealed ampoules. At low reaction temperature, diphenylcarbodiimide was surprisingly given together with N,N-diphenyluretidine-2,4-dione, the cyclic dimer of phenylisocyanate. And 1,3,5-triphenyl-4-phenyliminohexahydro-1,3,5-triazine-2,6-dione, carbodiimide and triphenylisocyanurate which is the cyclic trimer of phenylisocyanate were formed at higher reaction temperatures. But at around the room temperatures, we could get only triphenylisocyanurate. Triethylstannyldiphenylphosphine was acted as a catalyst for the formation of the above compounds