The attack, carried out by two men dressed as senior police officers on Monday, also wounded 25 people.
Iraqi ministers and the US ambassador were attending a police parade at the time of the explosions.
The two bombers, with explosives strapped to their bodies, struck within three minutes of each other at the rear entrance to the ministry in Baghdad as the parade took place about 400m away, security officials said.
The dead included a major responsible for ministry security.
A mortar shell was also fired, but it fell next door in the police academy, causing no damage.
Senior officials, including Bayan Baqir Solagh Jabir, the interior minister, Sadoun al-Dulaimi, the defence minister, and Zalmay Khalilzad, the US ambassador, were watching the annual celebration of the formation of the Iraqi police force.
A US embassy spokesman said he understood that Khalilzad was fine.
The ministry has been attacked on several previous occasions. It has become a symbol of hatred for Sunni Arab fighters who accuse it of running a Shia militia that targets the Sunni Arab community.
The ministry denies such charges.
In November, US troops found a bunker run by the interior ministry holding 170 prisoners, most of whom were Sunni Arabs, many showing signs of abuse and torture.