Aim To test the biocontrol potential of Penicillium oxalicum, a biocontrol agent against fungal diseases and against the potato cyst nematodes (PCNs), Globodera pallida and Globodera rostochiensis. Methods and Results We tested the effect of P.oxalicum on the nematode cysts under laboratory conditions or in soil microcosms. A reduction in the rate of G.pallida juveniles hatching by P.oxalicum was observed when root diffusates from the Monalisa' and the Desiree' potato cultivar were used (98 center dot 6 and 74 center dot 1% reduction, respectively). However, the rate of G.pallida juveniles hatching was not significantly reduced when root diffusates from the San Pedro' tomato cultivar were used. Penicillium oxalicum also significantly reduced the ability of the G.rostochiensis juveniles to hatch (30 center dot 9% reduction) when root diffusates of the Desiree' potato cultivars were used. Penicillium oxalicum treatment of the soil significantly reduced the number of G.pallida cysts that were recovered from the soil of each pot that contained the Desiree' potato cultivar. Conclusions Our results show that P.oxalicum is a potential biocontrol inoculant for protecting potato crops against PCNs. Significance and Impact of the Study Penicillium oxalicum has potential to be used in order to reduce PCNs.