Code-switching and code-mixing are considered dynamic conversational phenomena in interpersonal interactions, that is an alteration between two or more languages, dialectal variants, language registers, and it is an effective communicative strategy which Persian-English bilinguals consider a genuine thing in their ordinary speech practice. The focus of the present study is on the structural analysis of reverse code-switching between Persian and English that are known to be referred to two typologically different languages. Participants of the present research, all late bilinguals, reported on frequent use of code-switching (CS) and code-mixing (CM) in everyday language practice. CS/CM is quite normal and frequent among Iranian bilinguals, especially in informal settings where bilingual speakers can freely switch between their languages. Furthermore, the results revealed that Iranian bilinguals switch from English to Persian and in verso mostly at the lexical and the phrasal levels (intrasentential switching mode), but less frequently at the clausal or the sentence level (intersentential switching mode). The research states that there are some restrictions on inserting English verbs into the Persian syntactic frame: the Persian language is thought to be the matrix language and the preverbal part comes from English as the embedded language, such incongruity between the morphosyntactic structure and the verbal system of the Persian and English languages impose some constraints on the occurrence of switching codes between the pair of the languages under study.