|Millennium:||1st millennium BC|
|158 BC by topic|
|Gregorian calendar||158 BC|
|Ab urbe condita||596|
|Ancient Egypt era||XXXIII dynasty, 166|
|- Pharaoh||Ptolemy VI Philometor, 23|
|Ancient Greek era||155th Olympiad, year 3|
|Balinese saka calendar||N/A|
|Chinese calendar||壬午年 (Water Horse)|
2539 or 2479
— to —
癸未年 (Water Goat)
2540 or 2480
|Coptic calendar||−441 – −440|
|Ethiopian calendar||−165 – −164|
|- Vikram Samvat||−101 – −100|
|- Shaka Samvat||N/A|
|- Kali Yuga||2943–2944|
|Iranian calendar||779 BP – 778 BP|
|Islamic calendar||803 BH – 802 BH|
|Minguo calendar||2069 before ROC|
|Seleucid era||154/155 AG|
|Thai solar calendar||385–386|
−31 or −412 or −1184
— to —
−30 or −411 or −1183
Year 158 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Lepidus and Laenas (or, less frequently, year 596 Ab urbe condita) and the Sixth Year of Houyuan. The denomination 158 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.
- At the request of the Romans, Ariarathes V, king of Cappadocia, rejects a proposal from the Seleucid king, Demetrius I, for him to marry the sister of Demetrius I. In response, Seleucid forces attack Cappadocia and remove Ariarathes V from the Cappadocian throne. Demetrius I then replaces him with Orophernes Nicephorus, a supposed son of the late king, Ariarathes IV. With Ariarathes V deprived of his kingdom, he flees to Rome.
- Attalus II Philadelphus, the second son of Attalus I Soter of Pergamum, ascends the throne following the death of his elder brother, Eumenes II.
- Publius Rutilius Rufus, Roman consul, statesman, orator and historian (d. c. 78 BC)
- Eumenes II, King of Pergamum who has ruled since 197 BC and a member of the Attalid dynasty; a brilliant statesman, he has brought his small kingdom to the peak of its power and made Pergamum a great centre of Greek culture in Anatolia
- Emperor Kōgen of Japan, according to legend.