In situ transformation of 4,4'-Dibromobiphenyl (4,4'-DBB) in water was observed with hydrothermal diamond anvil cell (HDAC) up to 633 K. It shows that 4,4'-DBB dissolves in water to form a homogenous phase at the temperature of 588 K and thus subcritical water oxidation of 4,4'-DBB higher than the temperature can be a homogenous phase. To accelerate the oxidative degradation, some Mn-Ce-Co complex oxide nanoparticles of about 100 nm were prepared by co-precipitation hydrothermal method. The nanoparticles show enough stability and catalytic activity for oxidative degradation of 4,4'-DBB in subcritical water. The catalytic activation increases with some Co doping and as for the complex oxides of Mn1Ce1. Mn0.9Ce1Co0.1 Mn0.5Ce1Co0.5, Mn0.1Ce1Co0.9, and Co1Ce1, the Mn0.9Ce1Co0.1 presents the best activation. The main intermediate products of degradation are benzoic acid and phenol. The apparent activation energy (E-a) is 35.92 with 5% Mna(9)Ce(1)Co(0.1), as catalyst and 46.69 kJ/mol with no catalyst about the chemical oxygen demand (COD). (c) 2012 Elsevier B.V. All rights reserved.