Investigating the influence of the state language on the language usage of pupils whose native language is Hungarian in the classrooms with the Ukrainian language of instruction The Hungarians living in Transcarpathia are a minority community, so it becomes important for those who live in this community to be able to use their mother tongue, and thus strengthen their national identity. Children who use both languages simultaneously in their communication are more likely to use loanwords, code-switching, and code-mixing. Pupils who do not study in their mother tongue are more likely to use a non-standard version of Hungarian than those who have obtained their school-leaving certificate in the secondary schools with the Hungarian language of instruction. The aim of the research is to investigate the characteristics of pupils’ language usage resulting from the influence of the official language in the classrooms with the Ukrainian language of instruction. Furthermore, the extent to which the usage of Ukrainian and Russian languages influences the students’ language usage, and the frequency of Slavisms and code-switching in their language. The survey showed that a higher proportion of schoolchildren use Slavic loanwords, than those who study in their mother tongue. Keywords: effect of bilingualism, second language’ loanwords, code-switching habits, learning in the language of the majority, pupils whose mother tongue is Hungarian, questionnaire survey.