Abstract The Lake Burullus is one of most important lakes in north Delta of Egypt. It is exposed to huge amounts of contaminated drainage water contain serious pollutants especially Organophosphours. Diazinon is an organophosphorus pesticide widely used in agriculture. Evidence of diazinon residues in water has generated an urgent need to develop treatment systems for protected human health and the environment from damage. The aim of this work was the optimization of diazinon biodegradation from aqueous solutions by Aspergillus niger MK640786 using the response surface methodology. Aspergillus niger MK640786 was succeeded to reduce the diazinon at optimal conditions were as follows: temperature 30 °C, initial concentration 25 mg/l, pH 5 and within 7 days of incubation. Under these conditions, the degradation rate of diazinon was 82%. The half-life values of diazinon with strain Aspergillus niger were,3.8, 3.9,7.2,10.9 and 15.8 d − 1 respectively. In contrast, the t1/2 values of diazinon in the non-inoculated were 14.36549, 17.71808, 34.83199, 40.65586 and 47.8675 d − 1 respectively. We can conclude that Aspergillus niger has able to remove diazinon with the lowest cost and a high efficiency.