European Corn Borer (ECB - (Ostrinia nubilalis Hübner) is one of the most important pest on corn in Croatia. In the last decade corn production was on over 400 000 ha, in Eastern Croatia. Although ECB is present every year, with no such a low intensity, their control is not implemented. Corn is grown in monoculture, at 40% of cornfields, which also has influence on spreading of ECB. In the last ten years average attack of ECB was 51.5%; been done three different kinds of trials for controlling ECB. First trials were carried out in DeKalb hybrids, and ECB was controlled by Biobit XL, on the base of Bacillus thuringiensis Berliner. Intensity of attack was decreased for 46%. Second trial was carried out in ten hybrids, in order to determine the tolerance of hybrids against ECB. It was identified that several domestic hybrids (OSSK 382, OSSK 664 and BC 462) are tolerant to ECB. The third trial was carried out with GM hybrids. Experiments included Pioneer hybrids Evelina Bt, and Landia Bt. Intensity of attack at Evelina standard was 52%, while in Evelina Bt, ECB wasn't present at all. At Landia standard ECB was present on 98%, while in Landia Bt, intensity of attack was 21%. At both Bt hybrids, number of larvae and tunnels was lower comparing to standard hybrids. Length of damage in Landia check was 20.66 cm, while in Landia Bt it was 0.45 cm. The yield was increased for 10.27% at Evelina Bt, and for 26.67% in Landia Bt comparing to their standards. This kind of experiments will be continued in the future, not only because of its agronomic importance, but also because of its ecological relevance.