The purpose of this study is to investigate the impact of the introduction of powder modifier into composite reinforced with carbon fabric on selected mechanical properties. The tests were performed on 16 groups of hybrid epoxy composites, including one reference group and 15 groups containing alumina with the grain size of F220, F240, F280, F320 and F360, added in the weight percent of 5%, 10% and 15%. This composite was made of certified components designed for application in the aviation industry. Test results indicated that an increase of alumina content by weight caused a decrease of strength of polymer composites in most tests. In addition, the value of the force transferred by the composite in the tensile test increased disproportionately to the cross section, which resulted in decreased strength, while the addition of alumina impeded the super-saturation of the carbon fabric, which caused discontinuities in the matrix material.