| Church: | Church of Constantinople |
| Archbishop Of: | Ecumenical Patriarch of Constantinople |
| Term: | 12 April 996 – 24 August 998[1] |
| Predecessor: | Nicholas II |
| Successor: | Sergius II |
| Birth Date: | ? |
| Death Date: | 24 August 998 |
Sisinnius II (Greek, Modern (1453-);: Σισίννιος|Sisinnios; died 24 August 998) became Ecumenical Patriarch of Constantinople in 996 and held the post until his death in 998.
According to the histories of John Skylitzes and Zonaras, he was extremely well educated, particularly in medical matters, and had been honoured with the office of magistros.[1] He was elected to the patriarchate on 12 April 996, after the see had remained vacant for four years, due to the preoccupation of Emperor Basil II with his wars against the Bulgarians.[1]
On 21 February 997, he issued a tomos on prohibiting marriage between persons related to the fifth or sixth degree. These regulations are soon after attested in juridical decisions, but appear to have also caused some opposition (Logos Antirrhetikos of Skribas Nikolaos,).[1] Two other canons on prohibitions related to marriages are also attributed to him, but are considered as fake by modern scholars.[1] A later note in Skylitzes' account also reports that Sisinnius managed to finally lay to rest the quarrels of the Tetragamy affair of Leo VI the Wise .[1] In 997/8, he also issued a typikon concerning the provision of the Metropolitan of Alania in the patriarchal monastery of Epiphanios in Kerasus.[1] Sisinnius was also the recipient of three letters from Leo of Synada.[1]
He died on 24 August 998. His successor was Sergius II of Constantinople, who was elected in 1001.[1]