Under the Sultans Mehemmed II and Suleyman the Magnifiscent, the Ottoman scholars and thinkers were familiar of the scientific achievements in Western World. But from the middle of the XVI th Century on, Ottoman scholarship sank deeply in Muslim Scholastic. Nevertheless some scholars of the XVII th Century, as Kâtip Çelebi and Hezarfen Hüseyin Efendi, realised the importance of Western science and krıowledge. Ali Aziz Efendi (d. 29 October 1798 at Berlin), the Ottoman resident ambassador sent in 1797 to Prussia, was the first Turkish thinker to get in touch with Western thought. The correspondance exchanged between Ali Aziz Efendi and the German orientalist Friedrich von Diez, found by the Author in Westdeutsche Bibliothek, Marburg/Lahn (Orientalische Abteilung, Ms Diez A quart 129) throws light on it. At the beginning, von Diez aimed only in receiving explanation about linguistic problerns. But later, he asked Ali Aziz Efendi some questions concerning philosophic and scientific matters. This were on the nature of the sun, the gender of the things, the relation of the electricity to the lightning, etc... The Ottoman ambassador answered in a booklet, which is unfortunately lost. Meanwhile it is possible to have some ideas on it from von Diez's critics. This clearly shows us that the Ottoman thinker had alm.ost no ideas on the experimental sciences and the rational philosophy of "the Enlightenment".