|Millennium:||1st millennium BC|
|Centuries:||3rd century BC – 2nd century BC – 1st century BC|
|Decades:||130s BC 120s BC 110s BC – 100s BC – 90s BC 80s BC 70s BC|
|Years:||106 BC 105 BC 104 BC – 103 BC – 102 BC 101 BC 100 BC|
|103 BC by topic|
|Gregorian calendar||103 BC|
|Ab urbe condita||651|
|Bahá'í calendar||−1946 – −1945|
|English Regnal year||N/A|
|Chinese calendar||丁丑年 (Fire Ox)
2594 or 2534
— to —
戊寅年 (Earth Tiger)
2595 or 2535
|Coptic calendar||−386 – −385|
|Ethiopian calendar||−110 – −109|
|- Vikram Samvat||−46 – −45|
|- Shaka Samvat||N/A|
|- Kali Yuga||2999–3000|
|Igbo calendar||−1102 – −1101|
|Iranian calendar||724 BP – 723 BP|
|Islamic calendar||746 BH – 745 BH|
|Minguo calendar||2014 before ROC
|Thai solar calendar||441|
|Wikimedia Commons has media related to 103 BC.|
Year 103 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Marius and Orestes (or, less frequently, year 651 Ab urbe condita). The denomination 103 BC 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.
- Gaius Marius prepares a campaign against the Ambrones and Teutones under king Teutobod who are settled in Gaul.
- Tryphon and Athenion lead the Second Servile War in Sicily.
- Alexander Jannaeus succeeds his brother Aristobulus I as king and high priest of Judea, until 76 BC.