The synthesis of N,N'-dimethylurea from monomethylamine and carbon dioxide is compared with the past works on the synthesis of urea from ammonia and carbon dioxide. They are quite similar, except the former is more favorable from the chemical equilibrium viewpoint but kinetically slower than the latter. Based on the similarity, some general treatments of the multicomponent-multiphase reaction and a speculation for the reaction mechanism applicable also for the urea synthesis is made. Introduction Organic cationic polymers are known to be effective floccurants for the spent eflluent water from fish processing plants. We have attempted to synthesize one from dimethylurea (DMU) and formaldehyde by polycondensation. Unfortunately, the products were in large part, of a cyclic nature, for example, tetramethyldimeh 1 d · 'd CHs-N-CH..-N-CHs d . ill f lin od t t Y ene lurel , I I ,an no SIgn cant amount 0 ear pr uc s were CHs-N-CH2-N-CHs obtained. We have now synthesized DMU from monomethylamine (MMA) and carbon dioxide, which is of interest in connection with urea (U) synthesis, which, in turn, provides another method for synthesizing soluble floccurant polymer. Since Bassarov's discovery of U synthesis reaction in 1870, numerous work has been published, of which Matignon et aU), Krase et al.2), Clark et al.3), Frejacques4), Tokuoka5), Kitawaki et aI. 6), Sakai et aU), Kawasumi8) and Otsuka et al.9) are of particular interest from the chemical viewpoint. However, no papers, to our knowledge, except a patent granted to B.A.S.F.I0), have ever been presented on the synthesis of DMU, a close homologue of U. The reactions relevant to the DMU synthesis are: COa+2MMA = MAMCA MAMCA = DMU +HzO MAMCA+HaO = MAMCO MAMCO+COa+HaO = 2MAHMCO (a)