It is believed that there are three phases in the evolution of mankind's thought: Mythical period, philosophical period and scientific period (Kazzazi, 1993: 9-23). These various ideas have given birth to various outlooks on the world, human being, and God and have formed different worldviews. Mythical period and worldview was dominated in Greece from the very old time to the onset of philosophical thought period, but in 6th century B.C. with the appearance of different philosophers with miscellaneous ways of thinking this worldview went into the unconscious. The result was the evolving of a new worldview which was in turn known as philosophical thought. Thales of Miletus is the pioneer in this thought period. Introducing the notion of substance, he put the first step forward in bring down the mankind's thought. This way of thought had lasted until Renaissance when we witness the birth of scientific thought period to the time being. The main important characteristics of philosophical thought cycle is the possession of heaven-earthen worldview. It is to say that human being feels that there is a Meta look or control over his life. He thinks his fate is pre decided and the natural disasters like floods and earthquake are the result of God's anger in skies. But he is also determined to find the earthen causes of diseases here on earth. He intends to know the causes of natural disasters; therefore he is after the earthen cause. The purpose of the present paper is to study Iran’s passage into the philosophical worldview which was carried out by Zarathustra. By an inductive method, the present study introduces Zarathustra’s ideas as the starting point of an essential change in the worldview and living of Iranians. With the dawn of these ideas, subjective thought and questions and knowledge of God raised in people’s minds gradually and this caused the mythological worldview to be pushed to the margins. Later, Zoroastrian priests, based on this new worldview, made Zoroastri
