Officers responded to reports of a stabbing at a parking lot near Country High School at about 9:55 p.m., according to Vacaville police.
Preliminary reports indicate the two victims were at the Fiesta Days festival when they were confronted by a group of five to seven males, police said.
The group challenged the 16-year-old victim to a fight, police said.
The teenager accepted, and when he arrived at the parking lot with his uncle, the two were attacked and stabbed multiple times, police said.
The two were taken to a hospital with injuries that were not expected to be life threatening.
No one was arrested.
Anyone who might have information about the incident is urged to call Vacaville police at (707) 449-5416.