Gerunds lead to great simplicity and functionality in the Turkish language while increasing the expressive power, enabling the expression to become more concise and fluent. In the Common European Framework of Reference for Languages (CEFR, henceforth), an accepted guide in teaching Turkish as a foreign language, the correct and effective use of gerunds and gerundial formations is accepted as one of the grammatical competencies required for learners in C1 level. However, a few studies in the literature have investigated the learners' success in C1 level regarding grammatical competence. Based on this literature gap, the purpose of the research is to examine the use of gerunds and gerundial formations in the written expressions of the Arab learners of Turkish as a foreign language at the C1 level. For this purpose, the research is designed as a qualitative case study. The study sample includes 150 Arab learners in the C1 level who studied at TÖMER in the Black Sea Region, Central Anatolia Region, and Marmara Region in the 2019-2020 academic year and voluntarily participated in the research. The research data were collected from the learners' written expressions in the final exam and analyzed using document analysis. The scope of the study only included gerunds and gerundial formations. Frequency analysis, one of the sub-techniques of content analysis, was used to analyze the data. The data revealed that the 150 learners used 32 different gerunds and gerund particles in their written expressions.