 This study analyzed the chemical and structural properties of hazelnut, pistachio, and apricot kernel shells ground into different sizes, and their composites with polyester matrix material were fabricated by adding varying amounts of these powder particles. The XRD analysis revealed cellulose structures in the powder particles, while FDIR analysis showed surface functional groups mainly caused by cellulose and hemicellulose structures. These structures affected humidity and ash ratios. Heavy metals such as SN, Ca, K, Na, Milligram, Fe, Ni, Mn, Cu, Zn, and Si were found in the powder particles. Powder particles added to the polyester material adversely affected tensile strength but positively impacted bending and compressive strength at low rates. This article was authored by Yahya Haman Selik, Rojin Yarsin, Tolga Topkaya, and others.