The sect owns Clonaid, a company that claims to have produced the first cloned human child.
Vorilhon, known as Rael, was detained for nine hours at Seoul’s Incheon International Airport before being forced to leave. He had arrived on a flight from Toronto, Canada.
“We banned him because his presence here may hurt our national interests or cause social disorder,” an unidentified South Korean ministry official told AFP.
Vorilhon was in Korea for a 17-day tour, which was scheduled to include lectures on human cloning.
Followers of the Raelian sect believe that cloning is the secret to eternal life.
Vorilhon claims that on the 13 December 1973, he was contacted by a visitor from another planet, and asked to establish an alien embassy on Earth in preparation for their return.
Clonaid has a subsidiary in South Korea, and the Las Vegas-based company has said in the past that South Korean women have been the host mothers to cloned children.
As no scientists have been able to assess or examine a human clone, the Raelian claim that they have successfully produced one is accepted as very unlikely.
There are some 60,000 Raelian followers worldwide, the sect’s website claims.