The impacts of tourism development on environment of less- developed countries have become a controversial issue in recent decades. Some countries like Iran, in spite of having vast and rich natural, historical and religious sites, have taken a more conservative stance toward tourism industry. Others, on the other hand, have taken advantage of ever-growing tourism industry and keep an eye on its vast economic revenues with no or little concern about its environmental impacts on their societies. The aim of this study is a detail examination of environmental predicaments that many developing societies encounter in the process of tourism development. The article concludes that though tourism sustainable development may bring about economic wealth for host countries, policies have to make to avoid potential dangers threatening socio-cultural environment of these countries.