Al-Ghazali was one of the Islamic scholars who was interested in revivaling Islamic religious teachings and for this reason, he wrote Ihya -Ulum aI-Din. In this book, he tried to provide a pattern for the believers of his time. In this paper, with emphasis on psychological views of al-Ghazali, we try to discuss about effects of religiosity. For this purpose, Ghazali’s ideas, which has been expressed in four parts of Ihya’ ‘ulurn aI-din as ‘Ibadiyyat, ‘Adat, Munjiyat and Muhlikat, under the titles of epistemological, spiritual, emotional, moral and social effects ofre ligiosity, will be taken into consideration. As we know, the religiosity which is based on knowleldge depends on the answers to existential and Interpretative questions. For Believers, Saviors of religion (Munjiyat), In addition to the elimination of evils (Muhlikat), help to create positive emotional feelings. Ethics has a crucial role in religiosity. So believers in their own lives must try to acquire moral virtues and avoid moral vices. In al-Ghazali’s thoughts, religion provides happiness for believers both in this world and in hereafter.