Abstract: Interactions of three species of nematodes Aphelenchus avenae, Aphelenchoidessaprophilus and A. besseyi were investigated on potato dextrose agar in the presence of fungusAlternaria tenuis at different temperatures. Competitive interaction between the nematodes wasmeasured as decrease in numbers of animals when they were grown in mixed cultures. A. avenaewas the best competitor compared with A. besseyi and A. saprophilus at temperatures of 15-25ºCand 30ºC. The numbers of males of A. besseyi and A. saprophilus increased in the presence ofnematodes of other species. Temperature, reproduction rate and original properties of competitorsinfluenced interspecific interactions of the three nematode species.