A British defence ministry spokesperson said that two RAF Tornado aircraft fired Brimstone missiles at a van loaded with weapons and a transport vehicle west of the Iraqi capital of Baghdad.
The jets attacked IS targets for the first time Tuesday, four days after the British parliament approved airstrikes against the radicals in Iraq.
The warplanes fired four missiles after ensuring that the targets belonged to the IS.
The attacks were carried out successfully, according to the initial analysis, the spokesperson said.
Michael Fallon, British defence minister, said that the missions would continue to support the ground forces of the Iraqi army.
During Tuesday's raids, two Tornado GR4 aircraft attacked positions laden with weapons and an IS vehicle.
The RAF aircraft are only involved in combat missions against the IS in Iraq and not in Syria as the government in Baghdad had requested help from London to fight the militants.