Nowadays, most advanced industrial processes are performed at very high temperatures, these temperatures are higher than the melting point of many available materials. Knowing that the most of high temperature resistant materials are used in high-tech industries, these materials should have light weight and low densities. Hence, composite materials are good candidates for these applications. In this research, with respect to extensive application of carbon fiber reinforced composites in aerospace, military, automotive and other industries, carbon fiber reinforced phenolic composites have been chosen and nanosilica and graphene platelets are added to improve their mechanical properties and ablation resistance. In order to find optimal amount for these materials, response surface methodology (RSM) was used. Using this method, the effect of weight percentage of silica nanoparticles and graphene platelets on the flexural strength and ablation resistance of the samples were investigated. Analysis of variance (ANOVA) is performed on the resulting data and meaningful factors are recognized and their mathematical model is represented with respect to obtained results from ANOVA. To investigate the flexural strength of samples, three-point bending test and to evaluate ablation resistance of nanocomposite samples oxyacetylene flame test are used. The results show that the highest flexural strength and ablation resistance in samples occurs at 2.5 wt% silica nanoparticles and 0.7 wt% graphene platelets. Flexural strength of samples increased from MPa 52.8 MPa to 150 MPa, which shows a 184 percent improvement in flexural strength in comparison with the reference samples. These amounts of nanofillers also reduced the ablation rate of samples from 0.138 g/s to 0.0418 g/s which shows a 230% improvement in comparison with reference samples.The results of tensile strength also show that the optimum weight percent of the nanofillers will result in the highest amount of other mechanical properties. The microstructure of nanocomposite and reference composite samples is analyzed and compared. Investigation of the fracture surface of nanocomposite samples show that the incorporation of silica nanoparticles and graphene platelets, result in improvement of the adhesion between resin and fibers, and by increasing the amount of nanofillers, agglomeration occurs and due to agglomeration the mechanical strength is decreased. Also the microstructure and EDS analysis of the ablated surface of samples shows the formation of SiC on the surface fibers in different weight percents of nanosilica which leads to the improvement of ablation resistance of samples. Results obtained from TGA show that the optimized sample had a 10.5 percent increase in residual weight at 500 centigrade degrees in comparison with the reference samples. Keyword : Carbon-composite, Phenolic resins, Ablation resistance, Nano composite.