The woman was carrying a Vietnamese passport at the Kuala Lumpur International Airport, where she was arrested, Malaysia's police chief said, AFP reported.
The police chief 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.
South Korean intelligence believed Kim Jong Nam was poisoned, Reuters had reported on Tuesday (February 14).
Lawmakers said the spy agency told them that the young, unpredictable North Korean leader had issued a "standing order" for his half-brother's assassination and that there had been a failed attempt in 2012.
Joongang Ilbo, a South Korean newspaper, quoted an unidentified intelligence official as saying that Kim was “stung by a poisoned needle” and “died right at that spot”.
According to the spy agency, Kim Jong Nam had been living with his second wife in the Chinese territory of Macau, under Beijing's protection, the lawmakers said.
A Malaysian police source who had seen closed-circuit TV footage from the airport said a woman was involved in the attack.
"So far from the CCTV we can confirm it's a woman," the source said.
"If the murder of Kim Jong Nam was confirmed to be committed by the North Korean regime, that would clearly depict the brutality and inhumanity of the Kim Jong Un regime," South Korean Prime Minister Hwang Kyo-ahn said.
Several years ago, Kim Jong Nam was mentioned in local media to be a potential successor to his father, according to Joongang Ilbo.