After a period of study and research in this field in the Columbia University in United States, he returned to Iran and was in charge of preparing and compiling literature textbooks for high schools.

[4][2] In 1966, he went to the United States at the invitation of Professor Wilfred Cantwell Smith, a renowned Islamologist and Hinduologist and director of the Center for the Study of World Religions at Harvard University, where he researched the history of world religions and taught Persian literature and mystical texts in Persian.

[2][3][4] During these years he traveled to India several times to study the traditional methods of interpreting Hindu texts as well as to observe the situation and religious of the Indian Zoroastrians in Varanasi, Delhi and Mumbai.

Then he was transferred to the Faculty of Theology and Islamic Studies of the University of Tehran and served in the Department of Comparative Religions and Mysticism.

[4] After completing his mission and returning to Iran, he continued to teach at the Faculty of Theology and Islamic Studies of the University of Tehran and was in charge of the management of the Department of Religions and Mysticism for several periods.

[247][248][249][250][251][252][253][254][255][256] A documentary film about the life and scientific and cultural works of Dr. Fathollah Mojtabaei has been produced under the name of "How good it was that you were born (original title in Persian: چه خوب شد که بدنیا آمدید)", which has been broadcast in July 2019 via IRIB TV4 channel.