The composites materials are commonly known and used in industry for a long time. It is caused by composite material properties which combine the very good mechanical properties with low density. Mechanical properties of composite materials depend mainly from the applied reinforcing materials. In this paper the impact of type of reinforcing fabric on composites mechanical properties was investigated, while particular attention to the properties in relation to the density. The analyzed composites were made of epoxy resin reinforced with aramid, carbon and polyethylene fibers. The density measurement was made by the hydrostatic weighing method. The specific strength and specific modulus were calculated based on the experimentally determined mechanical properties of tested composites. The highest mechanical properties are obtained in case of composites reinforced with fabrics made of carbon fibers. Performed research showed that the composites reinforced by the fabric with a twill weave and made of Pyrofil TR30 S carbon fibers are characterized by the highest specific strength among the tested materials. The article also showed that the composites reinforced by the fabric with a twill weave and made of HR 12K carbon fibers are characterized by the highest specific modulus among tested materials.