The five men labeled the "Wolf Pack" were convicted of a lesser charge in relation to the assault on a young woman in Pamplona
A mass rally was held in Madrid on Friday after a gang of men labeled the "Wolf Pack" by media were granted bail after being accused of gang rape.
Women's rights groups and equality campaigners were outraged when the five were acquitted of gang rape and convicted instead of sexual abuse, a lesser charge.
Many in Spain see the 9-year sentences they received in April too lenient.
"We're demonstrating mainly because we think this is not a country for women," said one of the protest organisers Sara Naila. "When we heard about the court ruling yesterday, we were really afraid but we were also enraged and this rage transformed itself in events like the one today: collective fight., because this justice system doesn't protect us."
The men were accused of attacking an 18-year-old woman as she returned to her car during Pamplona's famed San Fermin bull-running festival in 2016.
The case sparked international outrage after prosecutors said the men filmed their attack and boasted about their actions.