The main objective of this study is to provide a syntactic and semantic analysis of the phenomenon of structural ambiguity in English and Arabic within the framework of transformational syntax. More specifically, the study explains the sources and types of structural ambiguity in English and Arabic and characterizes the similarities and differences between the two languages regarding this phenomenon. It should be pointed out that this study examines structural ambiguity in writing because written expressions are not accompanied by the vocal signals such as stress, pitch and juncture which help to clarify the meaning. The findings of this study have shown that English and Arabic exhibit some similarities and differences with respect to the phenomenon of structural ambiguity. On the one hand, English seems to be generally more productive with respect to this phenomenon mainly because Arabic has case marking, while English doesn't. Another reason for this has to do with subject/verb agreement and adjective/noun agreement in Arabic. On the other hand, the two languages exhibit significant similarities with respect to the sources and types of structural ambiguity. The findings of this study can help in the area of Arabic/English translation, as well as the area of language teaching.