The desert locust, Schistocerca gregaria is considered among the major insect pests damaging crops in large parts of the world. Due to their eco-friendliness and bio-persistence, entomopathogenic fungi, are preferred to control insects, at various stages of their life cycle. Mycotoxins are synthesized by fungi and released as secondary metabolites which are toxic to many insect species. This study aims to extract citrinin mycotoxin from the entomopathogenin fungus, Penicillium aurantiogriseum, isolated from the desert locust, S. gregaria and to study the effect of both conidial suspension and citrinin mycotoxin on the development of the 5th nymphs. Results showed that the effect of both treatments has similar course of approach; in inoculation by each treatment, with different concentrations, the mean percentage of mortality of 5th nymphs of S. gregaria increased significantly as concentrations increased. The lethal concentrations of 50% mortality (LC50) of insects inoculated with conidial suspension were 9× 104 conidia / ml and 18.9 µl /ml for insects inoculated with citrinin. While, lethal time for 50% mortality (LT50) was 2.4 and 4.3 days for both tests, respectively. Data concluded that the fungus P. aurantiogriseum presents a biopesticidal potential against the desert locust, S. gregaria.