Green composites were produced from various cationically cured natural oil-based resins and agricultural fibers. The natural oils and agricultural fibers of interest included corn, soybean, fish, and linseed oils and corn stover, wheat straw (WS), and switchgrass fibers. The effects of the types of natural oil and agricultural fiber on the structure and thermal and mechanical properties of the composites were studied using Soxhlet extraction, thermogravimetric and dynamic mechanical analysis, and tensile testing. The green composites, with agricultural fiber loadings of 75 wt %, have thermal stabilities up to 275 degrees C. The Young's moduli and tensile strengths of the composites ranged from 1590 to 2300 and 5.5 to 11.3 MPa, respectively. In general, an increase in the degree of unsaturation of the natural oil resulted in improvements in the thermal and mechanical properties of the composites. The WS fibers tended to give composites with the best thermal and mechanical properties. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1392-1400, 2012