Manufacturing of high performance polymer-matrix composites is normally carried out by mean of autoclave using prepreg tapes staked and consolidated under the simultaneous application of pressure and temperature. Many parameters could influence the quality of prepared composites namely, curing pressure, curing temperature, curing time, and vacuum pressure. These parameters must be carefully used to generate good composites with high mechanical properties and reduced porosity. The effect of vacuum on resin infiltration inside the carbon fibers meshes, the viscoelastic properties of the resin as well as thermal cycles will be discussed.