RCMP say six-year-old Taya Meisel and her 12-year-old sister Talisha were picked up at their school in the hamlet of Brant near Vulcan Monday morning.
Officials are looking for their biological mother Trina Meisel.
RCMP say it was a parental abduction, as she does not have legal guardianship of the children.
Meisel, 48, is believed to be driving a 2007 black Honda CRV with Alberta licence plate of ORNRSE.
Police say they don't believe the girls are in immediate danger, but think they may have been taken to Vancouver Island.