By Agence France-Presse
Inspector General Khalid Abu Bakar said in a statement she was arrested at Kuala Lumpur International Airport.
The victim, killed Monday at the airport, has been identified by rival South Korea as Kim Jong-Nam, the estranged half-brother of North Korean supremo Kim Jong-Un.
Khalid said the arrested woman had a Vietnamese passport in the name of Doan Thi Huong born on May 31, 1988.
The suspect was "positively identifed from the CCTV footage at the airport and was alone at the the time of arrest," Khalid added.