Tarih-i Vassaf is a five-volume book was written by Abdullah Vassaf, who was in Divan service of Ilkhanid state in 728 (1328). There is important information related to the period of Gazan Han. The Arabic, Persian, Turkish and Mongolian words and terms in the work written in a very fancy style make it difficult to understand the text. For this reason, the Ferheng-i Vassaf dictionary containing the words that are difficult to understand was arranged. The dictionary was written by Nazmîzade Hüseyin in 1118 (1706). This dictionary contains some deficiencies and mistakes. In this study, after was given the information about the work, was emphasized the mistakes in Ferheng-i Vassaf.