The aim of the master’s thesis Islamic Mathematicians during Mongol Rule is to get a better insight into contributions of Islamic Mathematicians from the 13th to the 15th centuries. This text begins with short reviews of the history of trigonometry and the Mongol Empire. The introductory chapter also reviews the history of mathematics in the medieval Islamic world, in order to be able to follow further developments more easily. Islamic mathematicians during the Mongol time wrote papers about various areas such as mathematics, ethics, physics, philosophy, astronomy… Their achievements are briefly described in the chapter which contains their biographies. Important contributions in mathematics are highlighted in the third and fourth chapters. During this period the majority of papers dealt with trigonometry. Papers written by al-Kāšī and aṭ-Ṭūsī were especially important. Al-Kāšī’s trigonometric tables and iterative method, as well as aṭ-Ṭūsī’s proof of the law of sines, are great contributions to mathematics. Their work is also important for algebra, especially their papers on binomial coefficient. Al-Fārisī, who also made an important contribution to algebra, partly proved the fundamental theorem of arithmetic. The last chapter contains a conclusion in which the author gives her opinion.