|255 by topic|
|Ab urbe condita||1008|
|Balinese saka calendar||176–177|
|Chinese calendar||甲戌年 (Wood Dog)|
2951 or 2891
— to —
乙亥年 (Wood Pig)
2952 or 2892
|Coptic calendar||−29 – −28|
|- Vikram Samvat||311–312|
|- Shaka Samvat||176–177|
|- Kali Yuga||3355–3356|
|Iranian calendar||367 BP – 366 BP|
|Islamic calendar||378 BH – 377 BH|
|Minguo calendar||1657 before ROC|
|Seleucid era||566/567 AG|
|Thai solar calendar||797–798|
381 or 0 or −772
— to —
382 or 1 or −771
Year 255 (CCLV) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Valerianus and Gallienus (or, less frequently, year 1008 Ab urbe condita). The denomination 255 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.
- Sima Shi quells Guanqiu Jian and Wen Qin's rebellion.
- March 23 – Sima Shi passes away.
- Sima Zhao, Sima Shi's younger brother, inherits his brother's authority.
- Ma Jun, Chinese mechanical engineer from Cao Wei, invents the south-pointing chariot, a path-finding directional compass vehicle that uses a differential gear, not magnetics.
- January 6 – Marcellus I, bishop of Rome (d. 309)
- Dorotheus of Tyre, Syrian bishop and martyr (d. 362)
- Zhang Gui, Chinese governor of the Jin Dynasty (d. 314)
- Zuo Fen, Chinese poet of the Western Jin Dynasty (d. 300)
- February 23 – Guo Huai (or Boji), Chinese general
- March 16 – Guanqiu Jian, Chinese general and politician
- March 23 – Sima Shi, Chinese general and regent (b. 208)
- Fu Gu (or Lanshi), Chinese official and politician (b. 209)
- Liu Zan (or Zhengming), Chinese general (b. 183)
- Sun Luyu (or Xiaohu), Chinese princess