A close-up of the document reveals he was previously known as Sabourjian – a Jewish name meaning cloth weaver.
The short note scrawled on the card suggests his family changed its name to Ahmadinejad when they converted to embrace Islam after his birth.
The Sabourjians traditionally hail from Aradan, Mr Ahmadinejad's birthplace, and the name derives from "weaver of the Sabour", the name for the Jewish Tallit shawl in Persia. The name is even on the list of reserved names for Iranian Jews compiled by Iran's Ministry of the Interior.
Experts last night suggested Mr Ahmadinejad's track record for hate-filled attacks on Jews could be an overcompensation to hide his past.
Ali Nourizadeh, of the Centre for Arab and Iranian Studies, said: "This aspect of Mr Ahmadinejad's background explains a lot about him.
"Every family that converts into a different religion takes a new identity by condemning their old faith.
"By making anti-Israeli statements he is trying to shed any suspicions about his Jewish connections. He feels vulnerable in a radical Shia society."
A London-based expert on Iranian Jewry said that "jian" ending to the name specifically showed the family had been practising Jews.
"He has changed his name for religious reasons, or at least his parents had," said the Iranian-born Jew living in London. "Sabourjian is well known Jewish name in Iran."
A spokesman for the Israeli embassy in London said it would not be drawn on Mr Ahmadinejad's background. "It's not something we'd talk about," said Ron Gidor, a spokesman.
The Iranian leader has not denied his name was changed when his family moved to Tehran in the 1950s. But he has never revealed what it was change from or directly addressed the reason for the switch.
Relatives have previously said a mixture of religious reasons and economic pressures forced his blacksmith father Ahmad to change when Mr Ahmadinejad was aged four.
During this year's presidential debate on television he was goaded to admit that his name had changed but he ignored the jibe.
However Mehdi Khazali, an internet blogger, who called for an investigation of Mr Ahmadinejad's roots was arrested this summer.
Mr Ahmadinejad has regularly levelled bitter criticism at Israel, questioned its right to exist and denied the Holocaust. British diplomats walked out of a UN meeting last month after the Iranian president denounced Israel's 'genocide, barbarism and racism.'