Investigators said the boy found his mom and his dad fighting at their home on 6th Street Monday night.
The boy allegedly grabbed a pocket knife to defend his mom, and ended up stabbing his 42-year-old father.
The 42-year-old man was taken to UTMB with non-life threatening injuries.
It was not immediately clear where the man had been stabbed.
Child Protective Services and Santa Fe police are investigating.