Al-Megrahi was convicted in the 1988 bombing of a Pan American plane over Lockerbie, Scotland.
Gadhafi, speaking at a school in London, blamed former U.S. President Ronald Reagan and former British Prime Minister Margaret Thatcher for the bombing, which killed 270 people.
Gadhafi said the bomber's family will file the lawsuit once al-Megrahi dies from prostate cancer, The Guardian reported.
Al-Megrahi was released from prison in August 2009 on compassionate grounds. Doctors said he had just a short time to live. His release was widely criticized.
"After he passes away his family will demand compensation because he was deliberately neglected in prison," Gadhafi said. "His health was not looked after in prison, and he didn't have any periodic examinations. I wish him a long life. He was released because he was considered dead, and yet he was still alive."
Gadhafi said Reagan and Thatcher conspired to blow up the plane.
Gadhafi made the claim while speaking to students and teachers at the London School of Economics in a live video-link. It was reported the interview was arranged through Gadhafi's son, who received a doctorate degree there.