Reading and understanding scientific texts is difficult, both because it needs some background knowledge and because of the way they have been written or translated. Therefore, it would be an important matter to have a readable text especially for students to understand it easily. One of the most important factors to have a more readable text is the cohesion of that text, which can be obtained through the proper use of cohesive devices. This research was set out to investigate the influence of

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... ohesion on readability and as a result, on comprehensibility of the texts. For this purpose, four chemistry textbooks were used. Parts of the books were randomly translated by three groups of translators. The first group involves people who studied translation both in bachelor and master, the second one includes people who studied a field of science in bachelor course and translation in their master course, and the third group includes people who studied a field of science in both bachelor and master. The use of cohesive devices on these groups of translated texts was evaluated based on Baker's (1992) taxonomy of translation, and by using chi-square tests the difference in their were measured. Four readability formulas were used to measure readability levels of the texts, and an ANOVA test determined if there is a significant difference between them. Finally, by using techniques such as cloze test, retelling and personal response, chemistry students' comprehension of the texts was evaluated. The results revealed that although there is no significant difference between the use of cohesive devices in three groups of translations, the texts translated by SaTs were more difficult to read and less comprehensible than the texts translated by ST and GT. Due to these findings, the results hopefully, can be useful to suggest establishing translator-training courses for special purposes.