Properties of polyacrylonitrile (PAN) type carbon fiber reinforced cementitious composites were tested after aging in water at 20 and 60°C for up to 10 and 7 months, respectively. Composites with water-binder ratios of 0 25 and 0 40 and silica-fume contents of 0-28% were investigated. The results show an increase in flexural strength and toughness with time up to a maximum at two-four weeks, and a reduction thereafter, with a loss of up to 65% of the maximum value. The loss was higher at 60°C aging temperature and at higher silica-fume contents. Flexural strength and microhardness tests of the matrix showed a continuous increase with time, in agreement with observations of densification of the matrix and refinement of the pore structure, as observed by mercury intrusion porosimetry (MIP) tests.Maximum flexural strength and toughness values at early ages were obtained with mixes containing 7-14% of silica-fume. Higher silica-fume contents led to reduction in the early age strength and toughness values, although the matrix became denser and exhibited finer pore structure.SEM observations of the fractured specimens after loading showed crumbling of the matrix near inclined fibers, suggesting that fiber bending rupture is a major mechanism responsible for loss in mechanical properties which accompanied the densening of the matrix with increase in silica-fume content and age.