This paper examines the effects of thickness on the mechanical properties of LIGA Ni MEMS structures plated from sulfamate baths. The as-plated LIGA Ni specimens of different thickness (50 mum, 100 mum and 200 mum) were utilized in the microtensile experiments. Optical microscopy, orientation imaging microscopy and scanning electron microscopy were used to characterize the microstructure of the LIGA Ni specimens. Fracture Modes obtained from specimens with different thickness were revealed by scanning electron microscopy. The effects of specimen thickness are then discussed within the context of strain gradient plasticity theories. (C) 2003 Kluwer Academic Publishers.