This work aims to study effects of glass fiber (GF) on mechanical properties of polypropylene (PP)/potassium hexatitanate whisker (SPTW) composites. The potassium hexatitanate whisker (SPTW) was modified by silane coupling agent KH550. The grafted maleic anhydride (PP-g-MAH) was used as the compatibilizer, and different percentage of GF was added in PP/SPTW to prepare PP/SPTW/GF composites by melt-blending method. The impact cross section structure was observed by SEM and the crystalline structure of PP composites was observed by XRD. Mechanical properties of PP/SPTW composites were investigated by comparing the effects of different percentages of GF with mechanical properties of PP/ SPTW composites. When the content of GF was 5%, the flexural strength, tensile strength and impact strength of the composites were the best and increased by 18.38%, 16.31% and 20.24%, respectively. The flexural strength of the composites began to decrease with the in-crease of the mass percentage of GF when the mass percentage of GF was more than 5%. GF can improve the mechanical properties of composites. With the increase of the content of GF, the mechanical properties of the composites increase and then decrease.