Composite insulating materials play an important role in the electrical equipment industry because of their balanced mechanical and electrical properties. Composite materials are totally homogenous and contain an organic material as binder and an inorganic material as reinforcing material. Any inhomogeneity is probably due to contaminations. In this study we deal with the type of contaminant resulting from chemical changes due to the reactions between the system constituents. Efforts were previously made to study the ageing behaviour of complex insulating materials. However, no major work has been done in the field of internal contaminants subjected to electrical stresses. This paper deals with investigations to determine the response of an internally contaminated composite due to voltage stressing. Ageing implies deterioration due to various types of stressing; electrical, environmental, thermal or mechanical, no matter what the type or stressing more or less all the properties get affected.