Interference fits are widely used in engineering applications. Many methods have been tried out to improve the strength of interference fits by improving the quality of the mating surfaces. An experimental investigation was carried out to study the strength of the assemblies after ball burnishing the shafts, which improves the surface finish and also imparts the surface strength by way of improving the hardness and residual compressive stresses. The assemblies were soaked for different duration times at elevated temperature and then the axial load-bearing tests were carried out in a Universal testing machine. The surface strengthening of shafts by burnishing and ageing of assemblies at high temperature resulted in considerable improvement of strength of the interference fit assemblies. This paper discusses the experimental investigations in detail and analyses the strength obtained from them. © 1992, Institution of Mechanical Engineers. All rights reserved.