Abstract: The coordination compound of cerium(Ⅳ) with PMBP(1-phenyl-3-methyl-4-benzoyl-pyrazolone-5), Ce(Ⅳ)A₄(A:PMBP), and its adducts, CeA₄·L(L=2, 2-dipyridine (Dipy), 1,10-phen-anthroline(Phen), tri-n-butylphosphine oxide(Tbpo) and triphenylphosphine oxide(Tppo) respectively) have been prepared. The molar conductiveties,thermogravimetric curves,IRspectra, electronic spectra and ¹H-NMR spectra were examined. These desired adducts, CeA₄·L, were confirmed by the above experimental data. The order of thermostability of adducts is CeA₄·Phen> CeA₄·Dipy>CeA₄·Tbpo≈CeA₄·Tppo.