The distribution of plant-parasitic and free-living nematodes on onion rhizospheres and plant material and their relationship with soil physicochemical properties was investigated in Karaman province. Plant and soil samples totalling 100 were collected from onion fields during July, 2012. Nematode population density per three plants and 100 g of dry soil were determined for each sample. Ditylenchus dipsaci (Kuhn 1857) (Tylenchida: Anguinidae) was found in 15% of plants and 61% of soil samples. Nematode numbers ranged between 0 and 140 (mean: 5) nematodes/three plants and 0-165 (mean: 33) nematodes/100 g dry soil. Other abundant plant-parasitic nematode genera were Paratylenchus (Micoletzky 1922) (Tylenchida: Paratylenchidae) (56%) and Tylenchus (Bastian 1865) (Tylenchida: Tylenchidae) (49%). The most abundant free-living nematodes were bacterivorous nematodes, which were found in 98% of samples, and were dominated by the Cephalobus (Bastian 1863) (Rhabditida: Cephalobidae) and Eucephalobus (Steiner 1936) (Rhabditida: Cephalobidae) genera. The majority of soil samples (68%) contained fungivorous nematodes belonging to the Aphelenchus (Bastian 1865) (Aphelenchida: Aphelenchidae) and Aphelenchoides (Fischer 1894) (Aphelenchida: Aphelenchoididae) genera. Omnivorous nematodes in the Dorilaimida order were found in 23% of soil samples. The distribution of plant- and bacterial-feeding nematodes were negatively related to the soil silt content and positively related to the soil sand content. Hyphal-feeding nematodes were negatively related to soil organic matter.