The mechanical behaviour of non-aged (modern) and aged spruce [Picea abies (L.) Karst.] wood was investigated in the radial direction using a microtensile testing device. The size of the samples was 50 3 3 mm (radial tangential longitudinal). Elastic, creep, relaxation, rupture and mechanosorption tests were carried out under controlled temperature and relative humidity. Optical and electronic micrographs were produced in order to correlate the mechanical behaviour with the wood structure. Results indicate that the overall mechanical properties such as Young's modulus and the timedependent behaviour of wood in the radial direction do not change significantly with age. However, the strength of aged wood shows a decrease of about 25% in the radial direction. This loss of strength in aged wood might be explained by localized damage at the microstructural level in the wood.