| Honorific-Prefix: | Mar |
| Shemon II | |
| Church: | Church of the East |
| See: | Seleucia-Ctesiphon |
| Patriarch Of: | Patriarch of the Church of the East |
| Patriarch of All the East | |
| Residence: | Mosul |
| Enthroned: | 1385 |
| Ended: | 1405 |
| Predecessor: | Denha II |
| Successor: | Shemon III |
| Birth Date: | 14th century |
| Death Date: | 15th century |
Mar II (sometimes written Shimun II) was the patriarch of the Church of the East from 1385 until 1405. He succeeded Denha II, who died in 1381/2, and his reign corresponds to the beginning of a period of obscurity in the Church of the East and the patriarchal succession.
He is mentioned in one near-contemporary list of patriarchs in a 15th-century manuscript copy of the Book of the Bee. He is listed between Denha II and Eliya IV, and the copy was produced in the time of Eliya's successor, Shemʿon III. The traditional listing makes Shemʿon III the successor of Shemʿon II and predecessor of Eliya IV, but the contemporary source is preferred.
Shemʿon II probably selected his name in honour of the 4th-century patriarch Shemʿon bar Sabbaʿe, a victim of the Forty Years' Persecution. Possibly he foresaw a similar period of persecution. His choice of name became very common thereafter. In view of the upheavals in Iraq in his time, it is unlikely that he was consecrated in Baghdad. Probably he was consecrated and resided in a monastery in northern Iraq. His reign fell in a period of intense persecution of Christians under the Timurid Empire. The 1390s saw a "flight to the mountains", as Nestorians took refuge from the upheavals in the region of Hakkari in northern Iraq. In 1401, Pope Boniface IX granted an indulgence to Greek Orthodox and Nestorian Christians who sheltered Latins fleeing the Timurids.