The use of hedging expressions is one of the important issues in academic writing. When a researcher states a claim, there is a possibility that his/her claim will be rejected by the academic community. Therefore, employing appropriate hedging devices can be a good strategy for this purpose. Due to the important role of hedging expressions in academic writing, this study attempted to investigate the use of hedging expressions in English and Persian MA and PhD theses. The results of this study showed some groups of hedges were used more than the other groups in the theses. Generally the total number of hedges was higher in English PhD theses compared to Persian PhD theses but it was not statistically significant. And the total number of hedges was significantly higher in English MA theses in comparison to Persian MA theses. It showed that in MA English theses students preferred more tentative style of writing.