|Centuries:||3rd century – 4th century – 5th century|
|Decades:||320s 330s 340s – 350s – 360s 370s 380s|
|Years:||352 353 354 – 355 – 356 357 358|
|355 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1108|
|Chinese calendar||甲寅年 (Wood Tiger)
3051 or 2991
— to —
乙卯年 (Wood Rabbit)
3052 or 2992
|- Vikram Samvat||411–412|
|- Shaka Samvat||277–278|
|- Kali Yuga||3456–3457|
|Iranian calendar||267 BP – 266 BP|
|Islamic calendar||275 BH – 274 BH|
|Minguo calendar||1557 before ROC
|Seleucid era||666/667 AG|
|Thai solar calendar||897–898|
Year 355 (CCCLV) was a common year starting on Sunday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Arbitio and Maesius (or, less frequently, year 1108 Ab urbe condita). The denomination 355 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- January 1 – Arbitio and Lollianus Mavortius begin their term as Roman consuls.
- August 11 – Claudius Silvanus, accused of treason, proclaims himself Roman Emperor. After 28 days, Ursicinus arrives from Rome and has Silvanus murdered.
- November 6 – Emperor Constantius II raises in Mediolanum (Italy), his cousin Julian the Apostate to the rank of Caesar. He takes command of the western provinces and marries Constantius' sister, Helena.
- The Lentienses, a Germanic tribe, are fined by the Roman commander Arbetio under Constantius II for several incursions against the Roman Empire.
- The Franks besiege Colonia Agrippinensium for ten months.
- The Huns of Central Asia begin their great drive westwards with an advance into Scythia (modern Russia). They overcome and absorb the Alans, a nomadic and warlike horse breeding people from the steppes northeast of the Black Sea.
- Pope Liberius refuses to sign a condemnation of Athanasius, Patriarch of Alexandria, imposed at Milan by Constantius II. Liberius is exiled to Beroea (Greece) and replaced by Felix II. He becomes an antipope and bishop of Rome.
- Fan Tai, Chinese general during the Jin Dynasty (d. 428)
- Murong Bao, emperor of the Xianbei state Later Yan (d. 398)
- Aedesius, Neoplatonist philosopher
- September 7 – Claudius Silvanus, Roman usurper
- Fú Jiàn, emperor of the Di state Former Qin (b. 317)
- Empress Liang, wife of Chinese emperor Fu Sheng
- Zhang Yaoling, ruler of Former Liang (b. 344)
- Zhang Zuo, Chinese ruler of Former Liang