The purpose of this study is to investigate the effects of prompt types on EFL learners’ writing performance. 6 university students and 10 university students were provided with bare and prose prompts and the fluency of their writings was measured by analyzing the length of product (word count) and mean length of T-units (MLTU) was used to measure syntactic complexity. Furthermore, independent T-tests were administered in addition to qualitative analysis in order to determine whether the differences between the two types of prompts were significant. The results showed that while high school students’ writing wrote longer texts and had higher MLTU on the prose prompt than the bare prompt, a large portion of their writing was copied from the prompt when they were provided with the prose prompt. The university students’ writing showed that they wrote longer texts and had higher MLTU on the bare prompt than the prose prompt. In addition, they had responded after the test that they were able to write more freely when they were given the bare prompt. The findings of this study suggest that test developers need to consider the effects of prompt types and examine the quality of the writings more carefully.