Menggu Ziyun (Chinese: 蒙古字韻, "Rimes in Mongol Script") is a 14th-century rime dictionary of Chinese as written in the 'Phags-pa script that was used during the Yuan dynasty (1271–1368). The only surviving examplar of this dictionary is an 18th-century manuscript copy that belonged to Stephen Wootton Bushell (1844–1908), and is now held at the British Library (Or. 6972). As the only known example of a 'Phags-pa script dictionary of Chinese, it is important both as an aid for interpreting Yuan dynasty texts and inscriptions written in Chinese using the 'Phags-pa script, and as a source for the reconstructed pronunciation of Old Mandarin.