He was first placed in-charge of the first Royal Hospital at Ray, from where he soon moved to a similar position in Baghdad where he remained the head of its famous Muqtadari Hospital for a long time. He moved from time to time to various cities, specially between Ray and Baghdad, but finally returned to Ray, where he died around 930 A.D. His name is commemorated in the Razi Institute near Tehran.

Razi was a Hakim; an alchemist and a philosopher. In medicine, his 'contribution was so significant that it can only be compared to that of Ibn Sina. Some of his works in medicine e.g. Kitab al-Mansoori, Al-Havi, Kitab al-Mulooki and Kitab al-Judari wa al-Hasabah earned everlasting fame. Kitab al-Mansoori, which was translated into Latin in the l5th century A.D., comprised ten volumes and dealt exhaustively with Greco-Arab medicine. Some of its volumes were published separately in Europe. His al-Judari wal Hasabah was the first treatise on smallpox and chicken-pox, and is largely based on Razi's original contribution. It was translated into various European languages. Through this treatise he became the first to draw clear comparisons between smallpox and chicken-pox. Al-Havi was the largest medical encyclopedia composed by then. It contained on each medical subject all important information that was available from Greek and Arab sources, and this was concluded by him by giving his own remarks based on his experience and views. A special feature of his medical system was that he greatly favored cure through correct and regulated food. This was combined with his emphasis on the influence of psychological factors on health. He also tried proposed remedies first on animals in order to evaluate in their effects and side effects. He was also an expert surgeon and was the first to use opium for anesthesia.

In addition to being a physician, he compounded medicines and, in his later years, gave himself over to experimental and theoretical sciences. It seems possible that he developed his chemistry independently of Jabir Ibn Hayyan. He has portrayed in great detail several chemical reactions and also given full descriptions of and designs f or about twenty instruments used in chemical investigations. His description of chemical knowledge is in plain and plausible language. One of his books called Kitab-al-Asrar deals with the preparation of chemical materials and their utilization. Another one was translated into Latin under the name Liber Experimentorum, He went beyond his predecessors in dividing substances into plants, animals and minerals, thus in a way opening the way for inorganic and organic chemistry. By and large, this classification of the three kingdoms still holds. As a chemist, he was the first to produce sulfuric acid together with some other acids, and he also prepared alcohol by fermenting sweet products.
His contribution as a philosopher is also well known. The basic elements in his philosophical system are the creator, spirit, matter, space and time. He discusses their characteristics in detail and his concepts of space and time as constituting a continuum are outstanding. His philosophical views were, however, criticized by a number of other Muslim scholars of the era.

He was a prolific author, who has left monumental treatises on numerous subjects. He has more than 200 outstanding scientific contributions to his credit, out of which about half deal with medicine and 21 concern alchemy. He also wrote on physics, mathematics, astronomy and optics, but these writings could not be preserved. A number of his books, including Jami-fi-al-Tib, Mansoori, al-Havi, Kitab al-Jadari wa at-Hasabah, al-Malooki, Maqalah fi al-Hasat fi Kuli wa al-Mathana, Kitab al-Qalb, Kitab al-Mafasil, Kitab-al-'Ilaj al-Ghoraba, Bar al-Sa'ah, and al-Taqseem wa al-Takhsir, have been published in various European languages. About 40 of his manuscripts are still extant in the museums and libraries of Iran, Paris, Britain, Rampur, and Bankipur. His contribution has greatly influenced the development of science, in general, and medicine, in particular.