The black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), is almost a cosmopolitan pest in distribution. It is a polyphagous insect attacking nearly all vegetables and many economic field crops in the world. The present study was conducted to investigate the disturbing effects of entomopathogenic nematodes (EPNs), Steinernema carpocapsae and Heterorhabditis bacteriophora on the activities of phosphatases and transaminases in the haemolymph of A. ipsilon larvae.  The newly moulted penultimate (5^th) instar larvae had been infected with LC₅₀ values of S. carpocapsae and H. bacteriophora (21 IJs/ml and 62 IJs/ml, respectively) and the influenced enzymatic activities were determined in the haemolymph of last (6^th) instar larvae, at three-time intervals, 6, 24 & 48 hr, respectively. The most important results could be summarized as follows. The acid phosphatase (ACP) activity significantly increased in haemolymph of 6 hr-old last instar larvae of A. ipsilon. In contrast, ACP activity was remarkably decreased in 24 and 48 hr-old larvae. The alkaline phosphatase (ALP) activity increased in the haemolymph of 6 hr-old larvae. On the contrary, ALP activity was considerably reduced in haemolymph of 24 and 48-old larvae. Glutamic oxaloacetic transaminase (GOT) activity significantly increased in the haemolymph of 6 hr-old last instar larvae. In haemolymph of 24 hr-old larvae, GOT activity considerably increased by H. bacteriophora but was slightly decreased by S. carpocapsae. At the last time interval, GOT activity greatly decreased, regardless the EPN species. Glutamic pyruvic transaminase (GPT) activity was predominantly declined in larvae infected with S. carpocapsae or H. bacteriophora, at all-time intervals, with an exception of a slightly increased activity in 6 hr-old larvae after infection with S. carpocapsae. Moreover, GPT activity was increasingly reduced with the time intervals. Also, H. bacteriophora exhibited stronger reducing potency on the GPT activity than S. carpocapsae. In conclusion, the disturbances of activities of phosphatases and Transaminases, as a result of the interactions between these nematodes and their symbiotic bacteria versus the immune responses of the host insect, end in the host death. Therefore, the tested EPNs can be used as a part of the Integrated control program against A. ipsilon.