Adverbs require a great deal of effort to be mastered, and even the most advanced users of that language have difficulty in using them correctly (Narita & Sugiura, 2006; Peacock, 2010; Lei, 2012; Leedham & Cai, 2013). The purpose of this study is to find out to what extent relatively high proficiency level EFL learners use different types of adverbs in their argumentative essays. For this purpose, a group of students who have previously taken an academic writing course are selected. To collect the data, a guided writing activity is applied in the target language. The data is analyzed quantitatively by taking the frequency of adverb use. The results show that EFL learners tend to use degree adverbs more than any other semantic category of adverbs. They also tend to overuse adverbs in their academic writing and use adverbs that are not appropriate in the academic prose. It is implied that there is a need for systematic explicit instruction of L2 adverbs and for raising learners' awareness in the meanings and functions of adverbs in L2 writing.