This book is a report on the study of the effects of iron filings on some mechanical properties of iron filing-reinforced unsaturated polyester composite. Particulate iron filing-reinforced polyester composite of different weight percent (wt. %), varied from 0%, 5%, 10%, 15%, 20%, 25% to 30% were fabricated. Tensile, flexural, hardness and impact resistance tests were then carried out on the samples. Metallographic characterization was also done using an optical microscope as well as the scanning electron microscope to study the surface morphology of selected composite samples. Results showed marked improvements in the mechanical properties of the polyester composites. The research work was carried out in partial fulfillment of the award of Master of Science (M.Sc.) in Materials Science and Engineering, at the Obafemi Awolowo University, Ile-Ife, Nigeria.