Abstract: Knit ted GF/ PP composites were produced by hot-pressing knitted GF/ PP preforms made of GF/ PPcommingled yarns. Four groups of GF/ PP composites with different cooling histories were prepared by changing thecooling method used in the cooling stage. The crystal st ructure of the mat rix of GF/ PP composites with differentcooling histories was studied using X- ray diff raction method. It is found that the cooling conditions studied in thepaper have no effect on the crystal types of the PP mat rix. However , the crystal degree and the sizes of the microliteand the spherulite vary with the cooling conditions. They all tend to increase with the decrease of cooling speed andthe prolongation of the cooling time.