<p>This study investigated the effect of supplementary pollination on yield and nut quality in the ‘Çakıldak’ hazelnut cultivar. Mixtures of pollen from the previous year (PY) and the same-year (SY) pollen mix from promising hazelnut genotypes were utilized as the pollen source. The 2, 3, 5‑triphenly tetrazolium chloride test was used to determine pollen viability, while the agar method was employed to determine pollen germination. The PY pollen was kept in separate containers in a&#xa0;deep freezer at −18 °C. The results demonstrated that the SY pollen mixture viability in 2023 was 62.31%, and the PY pollen mixture was 36.59%; in 2024 it was determined to be 47.50% and 37.77%, respectively. In 2023, the germination rate in the pollen mixture of the SY at 15% sucrose concentration was 26.60%, and in the pollen mixture of the PY it was 18.60%; while at 20% sucrose concentration, it was determined be 42.10% and 18.28%, respectively. In 2024, at a&#xa0;15% sucrose concentration, the pollen germination rate for the SY mixture was 20.30%, and for the PY mixture, it was 19.40%; at a&#xa0;20% sucrose concentration, the rates were 32.20% for SY and 19.07% for PY. The effects of the applications on the nut set and the number of nuts in a&#xa0;cluster, which are the basic factors of hazelnut yield, were striking; the nut set varied between 73.50% and 93.47%, and the number of nuts in a&#xa0;cluster varied between 2.03 and 2.76. While the effects of the applications on some nut traits were statistically significant (nut weight, nut size, nut and kernel shape index, nut and kernel oblateness index, blank nut, oil ratio, palmitic and stearic acid), the effects on other traits were not found to be significant. The research revealed that supplementary pollination could increase the yield by 21.9%.</p>