Police were called to the 12100 block of Prairie Ridge Dr. E. in Bonney Lake just before 10:30 p.m., said officials with the Pierce County Sheriff's Office.
Investigators believe the son got into a fight with his mother, stabbed her in the back, then lit a mattress on fire.
Firefighters arrived and got the fire out quickly and got the mother to Good Samaritan Hospital in Puyallup, but her condition is not known.
The son had run from the home, but was captured nearby by deputies just after midnight, officials said.
Firefighters say fire damage was limited to the bedroom.