Composite sheets were made of cyclic butylene terephthalate as matrix and carbon fibers as reinforcing material.Hot press method was used at different temperatures for composite processing. The mechanical properties of these materials and the effect of processing temperature were tested. The samples were kept in a climate chamber, and the effect of air humidity was examined through the change of the mechanical properties. Pictures were taken by a scanning electron microscope of the broken surfaces of the specimens. The results give conclusions about the outdoor application of these composites.