Post-release monitoring of transgenic Bt maize fields for resistant pest populations is an important activity that will contribute to early identification and mitigation of resistance evolution by target pests. An effective Bt maize pest resistance monitoring programme relies on well-established baseline susceptibility data. The target pest of Bt maize in South Africa, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), has evolved resistance to Bt maize expressing Cry1Ab proteins, with numerous reports of resistance from the highveld region of the country. Although Bt maize has been cultivated in the Eastern Cape province since 2001, no data exist on the resistance status of field populations of B. fusca to Bt maize in this region. In view of this, B. fusca larvae were collected from fields in two Bt maize cultivating areas and a non-Bt maize cultivating area of the Eastern Cape for laboratory assays to determine the level of susceptibility of B. fusca to Bt maize. Rearing colonies of each population were established and neonate larvae from each population were used to infest non-Bt maize plants, and Bt maize of events MON810 and MON89034. All larvae maintained on MON89034 died within seven days of infestation. Survival of all B. fusca populations maintained on MON810 declined rapidly during the first seven days and was significantly (P<0.001) lower than larval survival on non-Bt maize. Similarly, mass of surviving larvae of all populations on MON810 from the first two weeks to the 21st day was significantly (P < 0.001) lower than the mass of larvae on non-Bt maize. These results indicate that fieldcollected populations screened in this study are still susceptible to Bt maize.