Dicumylperoxide (DCP) is one of the most used peroxides in the polymer industry. It has been reported that its thermal decomposition can result in runaway phenomena and thermal explosions with significant economic losses and injuries to people. In the present paper thermal behaviour of dicumylperoxide in cumene was investigated over the temperature range of 393-433 K under aerated and de-aerated conditions. The results indicated that when oxygen was present, the decomposition rate did not follow a simple pseudo-first order kinetic as previously reported in literature. A satisfactory fit of the experimental data was, in this case, achieved by means of kinetic expression derived under the assumption of an autocatalytic scheme of reaction. The reaction rate was, on the contrary, correctly described by a pseudo-first order kinetic in absence of oxygen. Under both aerated and de-aerated conditions, chemical analysis showed that the decomposition mainly resulted in the formation of acetophenone and dimethylphenylcarbinol with minor occurrence of 2,3-dimethyl-2,3-diphenylbutane. The formation of methane and ethane was also invariably observed while the appearance of cumylhydroperoxide as a reaction intermediate was detected under only aerated conditions. Therefore, two reaction schemes were proposed to explain system behaviour in the presence of oxygen and after its purging.