ENThe present paper provides the analysis of phraseological units used in academic style popular science texts. Both the usual and occasional usage of phraseological units partially reflecting the processes of evolution of academic language is researched. Phraseological units are analysed according to relations of components, functional types, and the manner of modification. Cases of phraseological modification (addition, substitution, permutation, deletion) show how phraseological units change formally or semantically and help to convey new ideas and notions in an artistic and interesting manner. Both usual and occasional phraseological units grant more expression, force and life to popular science texts, help to engage readers and invite them to focus their attention on the subject in question. Moreover, Lithuanian phraseological units used in popular science texts have not been essentially analysed yet.