This study aims at conducting a comparative study of modulation in Arabic and English. It attempts to give extensive description of modulation in English and Arabic. It tries to find out the aspects of similarities and differences of the meanings of modulation in the two languages. The outcomes show that there are some aspects of similarities in Arabic and English Languages at different parts of speech such as nouns, adjectives and adverbs. The results also show that there are some points of differences between the two languages. For example, English is mainly expressed by using modal verbs. In opposite, Arabic is mainly expressed by using lexical verbs in addition to using prepositional phrases to express the meanings of modulation