The influence of entomopathogenic fungi, Penicillium aurantiogriseum and its mycotoxin citrinin against the haemolymph of the 5th instar nymphs of Schistocerca gregaria (Forskål) were studied under laboratory conditions. This study aims to detect the changes of some biochemical parameters of haemolymph which are valuable in evaluating and predicting the pathogenic effect on S. gregaria. Results showed an effect of P. aurantiogriseum and its mycotoxin citrinin on haemocytes, phenoloxidase activity and haemolymph protein at 1st, 3rd, 5th, 7th and 9th days post application. Comparison between the two treatments revealed fluctuations in the mean total haemocyte count and detection of plasmatocytes, lymphocytes and granulocytes in different percentages in treated nymphs. Citrinin mycotoxin and P. aurantiogriseum disturbed the titre of phenoloxidase enzyme in all intervals after infection. Also, they decreased the total haemolymph protein content significantly during the five days post infection as compared to the control.