Particle size distribution (PSD) of fine and micro-aggregate is known to strongly influence the microstructure of cement mortar and paste.In the present study, three granular fractions of fine aggregate (fractal dimention varied from 2.94 to 2.01) and two granular fractions of micro-aggregate (fractal dimention from 2.83 to 2.1 1) were combined in different proportions in order to investigate the influence of the PSD of fine and micro-aggregate on the microstructure of cement mortar and paste.Strength testing was conducted at age of 28 days.The hydration products of cement mortar and paste were determined by X-ray diffraction (XRD) and atomic force microscope (AFM) techniques.It was found that the microstructure of cement mortar or paste could be related to the PSD of fine and micro-aggregate.