Video shows the so-called superhero "Phoenix Jones" running up to a group of people, then pepper spraying them.
When officers arrived, they arrested the 23-year-old on four counts of assault. They also confiscated his yellow and black custom-made crime fighting suit as evidence.
"Just because he's dressed up in costume, it doesn't mean he's in special consideration or above the law," said a Seattle police spokesman. "You can't go around pepper spraying people because you think they are fighting."
Jones told police he was trying to stop a fight between two men, but couldn't explain why four people including two women got sprayed.
And this isn't the first time this has happened. Police say several people have reported being pepper sprayed by Jones.
Jones has been the most public face of a group of vigilante crime stoppers to show up in Seattle in the last couple of years.
He was booked under the name Benjamin John Francis Fodor.
The Associated Press contributed to this story.