The first suspect, a 28-year old woman carrying a Vietnamese passport, was arrested on Wednesday morning.
Selangor state police chief Abdul Samah Mat told AFP that police were looking for more suspects, but he declined to elaborate.
Two women were reported to have attacked Kim Jong-Nam on Monday as he was about to board a flight to Macau where he has spent many years in exile.
CCTV images that emerged in Malaysian media, purportedly of one of the suspects, showed an Asian woman wearing a white top with the letters “LOL” emblazoned on the front.
North Korean embassy officials were seen visiting Kuala Lumpur hospital’s forensic department in a diplomatic vehicle on Wednesday afternoon and, again, overnight.
Police inspector-general Tan Sri Khalid Abu Bakar confirmed the arrest of the second woman.