Chromite, ultramafic and mafic rocks from Eldivan, Yapraklı, Ayli Dağ, Küre, Elekdağ and Kızılırmak in northern Turkey have been studied to determine their min- eral and whole-rock geochemical, and Re-Os isotope geo- chemical characteristics. Most of the studied peridotites dis- play depleted but commonly V-shaped chondrite-normalized rare-earth element (REE) patterns while some peridotites as well as pyroxenites from all areas exhibit light REE depleted patterns. Olivine (forsterite 82 to 92 mol%) and spinel (chro- mium number 13 to 63) in the studied peridotites exhibit a wide range of compositions. Compositions of spinels suggest that peridotites from Eldivan, Ayli Dağ and Küre experienced relatively large degrees of partial melting (~ 15 and 19 wt%), whereas those of the Kızılırmak area most likely reflect lower melting degrees (~ 4–6 wt%). Whole-rock and mineral chemical data indicate that the ultramafic rocks are similar to abyssal and supra-subduction zone peridotites. The ultramafic rocks of the investigated areas exhibit a wide range of 187Re/188Os (0.12 to 6.6) and measured 187Os/188Os (0.122– 1.14), while the basaltic rocks from Küre, Eldivan and Kızılırmak areas have high 187Re/188Os (128–562) and mea- sured 187Os/188Os (0.724–1.943). On the other hand, chromite from Eldivan, Elekdağ and Kızılırmak show high Os contents (21.81–44.04 ppb) and low 187Re/188Os (0.015–0.818) and 187Os/188Os (0.122–0.133). Re-Os model ages (TChur) for all analyzed samples yielded scattered ages ranging from Jurassic to Proterozoic. Overall, geochemical data are interpreted to reflect different degrees of partial melting, melt – rock inter- actions and metasomatic effects that produced a heteroge- neous mantle in a supra-subduction setting.