The aim of the study is to reveal the importance in language learning of such individual differences as the level of intelligence and language aptitude in the case of bilingual and monolingual language learners. To measure the participants’ intelligence the Cognitive Abilities Test was used, and in order to make judgments about the level of the participants’ language aptitude, the other test administered was the Hungarian Language Aptitude Test (MENYÉT) the test developed to measure native Hungarians’ language aptitude. From the research it turned out that there are connections between certain aspects of intelligence, language aptitude and second language learning achievement. However these connections were found only in monolingual learners. Further research would be important to find reliable answers to the questions of the study.