Family name Siwai (สีไว 
, Siwai 
) , all around the world, is a rare surname. The surname Siwai is characteristic of Thailand, where it is a rare surname, Pakistan, where it is an extremely rare surname, and Malaysia. Measured by absolute frequency, it is commonest in Thailand, Pakistan, and South Africa. More prevalently, Siwai is the forename as well as the last name.