[Objectives]  Spodoptera exigua (Hübner) (beet armyworm) is a global insect pest that feeds on various agricultural crops including vegetables, cotton, and ornamentals. The main methods to control S. exigua are using chemical pesticides which can negatively impact human health and the environment. Using biological control organisms such as Microplitis pallidipes Szepligeti can reduce pesticide applications. To investigate the physiological mechanism of the parasitization of S. exigua larva by the M. pallidipes by collecting hemolymph from parasitizated host larvae. [Methods]  We examined the activities of immune and protective enzymes using a microplate reader. [Result]  The results indicated that the activity of superoxide dismutase (SOD) in the hemolymph of larval S. exigua began to increase 1 day after parasitization (DAP) compared to the control with significant differences occurring 4-5 DAP. Catalase (CAT) activity in the hemolymphs were consistently higher in parasitized larvae compared to the control, significantly at 1, 4, and 5 DAP. Finally, peroxidase (POD)activity was also higher in parasitized larvae compared to the control, significantly at 1, 2, and 5 DAP. [Conclusion]  These results suggest that excess reactive oxygen species (ROS) generated in host larvae were scavenged by SOD, POD and CAT impeding for more successful development of M. pallidipes in the host larvae. Simultaneously, Phenoloxidase (PO) activity was significantly lower in parasitized larvae after 1 DAP while lysozyme (LSZ) activity was significantly lower 3-4 DAP in the same treatment. Together, these results suggest that changes immune and protective enzyme and activities following parasitism are involved in S. exigua immune responses against parasitization, and provide insights into the physiological mechanisms of M. pallidipes regulation of host responses.