This paper discusses the use of Persian in comparison with Dari, a dialect of Persian language used in Kerman, one of the cities of Kerman Province located in southeast Iran. It is based on a random selection of 47 subjects from different sex, age, and occupational groups of Zoroastrian people with different levels of education in seven Domains, i. e. family, friendship, neighborhood, transaction, education, government, and employment. In this study, the subjects were asked to determine which language they use in different Domains on Likert’s 4-point scale. After collecting the data by the use of a questionnaire with 30 situations in the seven Domains and analyzing them, the researcher concluded that there is a Persian-Dari diglossia in Zoroastrian speech community in which Dari functions as the Low language whereas Persian is the High one. As a matter of fact, Dari has been restricted to family Domain and the young generation has lost it to a large extent.