Agricultural by-products, such as wheat straw, corn stalks, and soybean stems, are low cost sources of biofibers, produced annually in abundant quantities in Ontario. These materials can be combined with plastics into biocomposites with a wide range of applications in industries such as automotive components, construction and packaging. In this research, we have characterized fiber from wheat and soybean stems with respect to particle size distribution, morphology, chemical composition on the surface, interaction with moisture and resistance to high temperature degradation. Such properties play important roles in the processing of thermoplastic composites. The methods we used for this characterization include thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), and light microscopy. This research will enable researchers in the future to identify the Ontario crop fiber genotypes that are best suited to plastic biocomposite applications.