The Big Five Personality Factor Theory evaluates personality according to the five main factors of extraversion, agreeableness, conscientiousness, neuroticism and openness. The present study therefore aims to adapt John, Donahue, and Kentle's (1991) the Big Five Inventory into Turkish. Validity and reliability studies concerning the BFI were conducted on 1153 university students. For language equivalency, the English and Turkish forms of the inventory were implemented at different times on the same group of students who were proficient in both of these languages. In order to test the reliability and validity of the inventory, its content validity, language equicalency, and internal consistency were calculated.