Abstract: The species biological form composition and their spatial distribution was studied in south of Iran using egg morphological characters. All three known biological forms of the species; An. stephensi stephensi (type), intermediate and Mysorensis occur in the country; however their distribution and roles in malaria transmission are varied in each province. In Hormozgan province, all three forms were present. The type and intermediate forms with respectively 90 and 10% frequency occurred in urban-coastal or semi urban/rural-plain areas where An. stephensi is highly dominant and is the sole vector of disease. Mysorensis was found only in rural-mountainous areas where malaria is transmitted by other vectors. This is in agreement with the conventional idea that type form is important only in urban settings. However, in Sistan and Baluchistan which is the most malarious region of the country, in various human settings (urban/rural) and different climates only Mysorensis form was found. In Fars (Kazeron) which was previously a malaria endemic area and An. stephensi was the major vector, only intermediate was found. The biological differences in feeding behaviour and the differing vectorial capacity that have been observed in south of Iran can be explained in terms of the availability or limitation of animals` hosts. The results of this study emphasize on independent studies in each region, precaution in generalization and on reconsidering the conventional view about An. stephensi biological forms in western outreaches of the Indo-Pakistan subcontinent.