The effect of various enzyme treatments on the mechanical properties of jute fiber-reinforced polyester composites was investigated in this study. Prior to composite production, jute fabrics were treated with pectinase, laccase, cellulase and xylanase enzyme solutions with varying enzyme mixtures and treatment time according to experimental design. The comparison of NaOH and enzyme-treated samples was also investigated. Jute fabric-reinforced polyester composite samples were produced using compression molding. The effect of enzymatic and NaOH treatment on fibers and fiber-matrix interface was investigated by scanning electron microscopy study. The mechanical properties of enzyme-treated and control (without enzyme treatment) samples were evaluated by means of tensile and flexural tests. It was observed that enzymes destroyed pectin, hemicelluloses and lignin substances from the fiber bundle interface which reduced the technical fiber diameter and hence increased the fiber aspect ratio. Therefore, a greater fiber-matrix interface area was created after enzymatic treatment, which facilitated better fiber-matrix adhesion and improved mechanical properties of the composites. The data indicated that enzyme treatment can be used as an effective, cheap and environmentally friendly fiber modification method for natural fiber-reinforced composite production.