More than 10 years after registration of the first Bt maize cultivar in Europe, there still exists a remarkable lack of data on effects on Lepidoptera which would be necessary for a complete and comprehensive environmental risk assessment. So far only very few European butterfly species have been tested in this aspect. In our study the effect of transgenic Bacillus thuringiensis (Bt) maize pollen (event Bt-176) on the development and survival of neonate larvae of the Peacock butterfly, Inachis io (L.) was for the first time shown. The results of our study suggest that the Peacock butterfly may serve as a model organism for assessing potential side effects of new developed transgenic Bt crops on non-target butterflies in a GMO environmental risk assessment. The study was done under laboratory conditions by exposing larvae of the Peacock butterfly to various pollen doses of transgenic maize event Bt-176 (cv. PACTOL CB) or the conventional isogenic maize (cv. PACTOL) using a no-choice test. Larvae feeding for 48 h on nettle plants (Urtica dioica) that were contaminated with higher pollen concentrations from Bt-176 maize (205 and 388 applied pollen.cm-2) suffered a significantly higher mortality rate (68 and 85% respectively) compared to larvae feeding on leaves with no pollen (11%), or feeding on leaves with pollen from conventional maize (6 to 25%). At lower Bt maize pollen doses (23–104 applied pollen.cm-2), mortality ranged from 11–25% and there were no apparent differences among treatments. The corresponding LC50-and LC90-values for neonate larvae of the Peacock butterfly were 187 and 448 applied pollen grains.cm-2 of Bt-176, respectively. Weight of larvae surviving consumption of Bt-176 maize pollen declined between 10 and 81% with increased pollen doses (r =  −0.95). The highest weight reduction (81%) corresponded to the highest pollen concentration (388 pollen grains applied.cm-2). Ingestion of pollen from the conventional maize hybrid did not have negative effects on larval weight gain or survival rate.