Vegetable fibers have an economic potential to be employed as polymer reinforcement. This is due to their low cost, biodegradability, recyclability, adequate mechanical properties, and because they come from renewable sources. The growing need for alternative materials that meet the demands of various industrial segments (aerospace, mechanics, automobile, petrochemistry, shipping, civil engineering etc) requires detailed investigations on their physical, mechanical, and chemical properties. Detailed information about the behavior of fibers in a polymer matrix can indicate whether they can produce a structural composite. This work investigated the mechanical and thermal properties of polypropylene (PP) samples containing 0%, 10%, and 20% (w/w) Luffa cylindrica fibers, as well as to analyze the morphology of the fibers before and after their processing with the polymer. The mechanical results of the composites showed that those plant fibers reduced the strain of pure PP, increasing its stiffness. Thermogravimetric trials revealed that the composite had its thermal stability reduced with an increase in fiber content.