The present research studies the phonological and phonetic adaptation of 1393 French loanwords in Persian. Then, Mo’een Farsi Dictionary and Great Edition of Sokhan Dictionary were used for the phonetic transcription of the words in the target language, following the International Phonetic Alphabet (IPA). Optimality theory developed by Prince and Smolensky (Optimality theory: Constraint interaction in grammar. Blackwell, 2004) was used for the analysis. OT holds that linguistic forms are the outcome of interaction among violable but universal constraints. These constraints include two families: faithfulness and markedness; the former serves to ensure that input and output forms are exactly the same, and the latter serves to evaluate the well-formedness of output candidates. We consider phonological adaptation in both vowels and consonants. Findings show that the phonological processes that occurred in the adaptation (vowels and consonants) are insertion, replacement, and deletion. Replacement is the most frequent phonological process in loanword adaptation.