In this paper the restraining effect of aggregates on autogenous shrinkage of cementitious materials is investigated by using different maximum aggregate sizes. Experimental studies were conducted to determine the restraining effect of aggregates on autogenous shrinkage of composites with a paste to aggregate ratio of 70 to 30 by volume percent. It was shown that the autogenous shrinkage is reduced by addition of aggregate, and this effect can be predicted using Pickett's expression. A comparison of the results of calculated autogenous shrinkage with that of experimental studies on cement paste, mortars, concrete, and also individual composites containing cement paste and different particle size of aggregate is presented. The use of the modulus of elasticity obtained from the meso-mechanical modeling gave satisfactory predictions in calculating the autogenous shrinkage of cementitious materials. The microstructural characteristics of samples were identified using their pore size distributions that were determined by mercury intrusion porosimetry tests. The results show that experimental and predicted values of autogenous shrinkage are in good agreements.