In the present investigation, the influence of the proportion of jute fiber: glass fiber and surface treatment on the tensile strength of a polyester matrix composite material, manufactured by the compression method, was evaluated. The proportion of jute fiber: fiberglass used in the evaluation were 1: 1; 2: 1; 3: 1; 4: 1; In addition, natural fibers were worked on long fibers, for synthetic fibers (fiberglass) they were woven bidirectionally; and analyzed the influence they have when the natural fibers are subjected to a surface treatment of mercerization, which was worked at two percentages of NaOH, 5% and 10%. All the specimens were manufactured by the compression method, and formed into 30 cm x 20 cm plates with a thickness of 0.5 cm; subsequently subjected to a cure of 72 hours. The tensile strength was evaluated according to the normal ASTM D-628-01. From the results obtained, it w...