A new method to investigate the mechanical properties of miniaturized single crystal copper specimen was developed. Machining of these samples was accomplished using an ion beam. The limitations inherent to the method due to defect generation by ion bombardment were investigated by microstructural investigation and mechanical testing. To ensure highly precise loading along with the possibility to monitor the acting deformation mechanisms during testing at high lateral resolution, a microindenter was installed in the vacuum chamber of a scanning electron microscope. Investigations on compression specimen with different crystal orientation and geometry demonstrated the constraints present in micro-compression testing, in particular at the interface between sample and punch. Therefore, a new method was developed to perform miniaturized tensile tests. This allows the systematic study of the influence of specimen dimensions and aspect ratio on the mechanical properties without the restrictions known from compression testing. Tensile specimen with high aspect ratio depicted no hardening and a weak size dependence of the flow stress, while for short gauge lengths a dramatic rise in flow stress and significant hardening was observed. This demonstrates the influence of the interface in micro-compression testing, causing dislocations to pile-up, with the resulting back-stress on the active sources contributing to the size effect.