The "Deposed Emperor" Jin Feidi 晉廢帝 (r. 365-371), personal name Sima Yi 司馬奕, courtesy name Yanling 延齡, was a ruler of the Eastern Jin dynasty 東晉 (317-420). He was a son of Emperor Cheng 晉成帝 (r. 325-342) and Lady Zhou 周氏. As a young person he held the title of Prince of Donghai 東海, and from 361 that of Prince of Langya 瑯琊. He also held some honorific titles, namely palace attendant (shizhong 侍中), cavalry general-in-chief (piaoji da jiangjun 驃騎大將軍), and Commander Unequalled in Honour (kaifu yitong sansi 開府儀同三司).
In 365, Emperor Ai 晉哀帝 (r. 361-365) died without an issue. Empress Dowager Chu 褚太后 therefore issued a decree regulating the succession. Sima Yi chose a the reign motto Taihe 太和 "Great Harmony". His empress was Ms Yu 庾, but regency was carried out by Commander-in-chief (da sima 大司馬) Huan Wen 桓溫 (312-373).
The Eastern Jin had not abandoned the idea to reconquer the north, and therefore, Huan Wen decided in 369 to bring an army of 50,000 into the field, to challenge the northern state of Former Yan 前燕 (337-370). Yet the imperial army was defeated in the battle of Fangtou 枋頭 (close to present-day Junxian 浚縣, Henan). This defeat contributed to Huan Wen's decision to prevent an eventual dismission by dethroning the emperor. On the pretext of "illicit affairs in the inner palace", he urged the Empress Dowager to issue a decree dethroning Sima Yi. He was demoted to the position of Prince of Donghai 東海, shortly later to that of District Duke of Haixi 海西縣公.
Huan Wen enthroned Sima Yu 司馬昱, who is known as Emperor Jianwen 晉簡文帝 (r. 371-372). Sima Yi resided in Wuxian 吳縣 (today's Suzhou 蘇州, Jiangsu), where he was strictly observed. In 272, a messianic leader named Lu Song 盧悚 appeared in the region of Pengcheng 彭城 (in the north of today's Jiangsu). Lu invited Sima Yi to participate in his movement with the promise to appeal to the Empress Dowager to make him emperor again. In spite of the warnings of his entourage, Sima Yi agreed. Yet Lu Song's rebellion was defeated by the imperial armies and the insurgent died. From then on, Sima Yi refused to go out and spent all his day with drinking and his women. The court in Jiankang 建康 (today's Nanjing 南京, Jiangsu) had almost forgotten him when he died.
Sima Yi was buried in Mound Wuling 吳陵 close to the other dynastic tombs. He was not given a posthumous title.