The mercuric polybromobenzoates, (C6Br2CO2)2Hg, (XC6Br4CO2)2Hg (X = p-F, p-Cl, p-Me, o-Me, p-MeO or m-MeO) and (2,6-Me2C6Br3CO2)2Hg, and phenylmercuric pentabromobenzoate have been prepared by reaction of mercuric acetate or phenylmercuric acetate with the appropriate polybromobenzoic acids. Thermal decomposition of (C6Br5CO2)2Hg, (XC6Br4CO2)2Hg, (X = p-F, p-Cl or p-MeO) and C6Br5C02HgPh in boiling pyridine gave the new polybromophenylmercurials (C6Br2Hg, (XC6Br4)2Hg and C6Br52Hg respectively, but similar treatment of (XC6Br4C02)2Hg (X = p-Me, o-Me or m-MeO) and (2,6-Me2C6Br3CO2)2Hg yielded pyridine complexes of the mercuric carboxylates. Mercuric p-methyltetrabromobenzoate underwent decarboxylation in boiling nitrobenzenelpyridine giving (p-MeC6Br4), Hg, but the method could not be extended to (0-Mec6-Br4-CO2)Hg or (2,6-Me2C6Br3, CO2)2Hg. Decarboxylation of XC6Br4CO2H (X = o-Me or m-MeO) was effected in molten mercuric trifluoroacetate giving, after treatment of the products with sodium chloride, the corresponding tetrabromophenylmercuric chlorides. All mercurials underwent cleavage with iodine or triiodide ions in hot dimethylformamide to give the corresponding iodopolybromobenzenes, and (C6Br5)2Hg was converted into C6Br5Hg (X = C1 or Br) by the corresponding mercuric halides in hot xylene/nitrobenzene. Thermal symmetrization of C6Br5HgX (X = C1, Br, or Ph) is detectable prior to melting, but (C6Br5), Hg is stable to at least 400°. The mass spectra of the polybromophenylmercurials are discussed.