The ability to know the rules of word formation in a language and to use these rules in the process of understanding and producing more complex words is part of language skills. In German, it is possible to derive words of different types and with various meanings with morphemes with suffixes such as -keit, -ung, -ig, -lich. In this study, mixed research method was used in which both quantitative and qualitative data collection methods were used together. The study aimed to answer the following questions: What are the top ten most frequent words derived with the morpheme -keit in the DeReKo corpus? What are the significant conclusions from the data obtained from the frequency analysis of the DeReKo corpus? What is the importance of frequency analysis in the context of German as a Foreign Language? What is the importance of corpus-based studies in the context of German as a Foreign Language? In this study, first of all, the frequency of words derived with the statistically significant morpheme -keit was investigated through frequency analysis in the DeReKo corpus. According to the results of the frequency analysis in DeReKo, the top ten words with the highest frequency are “Möglichkeit, Möglichkeiten, Öffentlichkeit, Tätigkeit, Schwierigkeiten, Aufmerksamkeit, Wirklichkeit, Unabhängigkeit, Fähigkeiten and Notwendigkeit”. Finally, the importance of corpus-based studies and frequency analysis for GFL is emphasized.