The 28-year-old died after a bull’s horn pierced his lung and heart during a run in the southeastern village of Pedreguer near Valencia, a spokesman for the regional government said.
The bull caught him as he was trying to help another runner in the annual event, in which a man also died last year.
Many Spanish towns hold summer festivals involving bulls.
San Fermin, in which bulls chase red-scarved runners through Pamplona’s cobbled streets during nine days of events, is the most famous and attracts thousands of revelers from Spain and overseas.
In Saturday’s run there, a 33-year-old Japanese man was gored in the chest and a 24-year-old Spanish man in the arm, while 12 others suffered minor injuries, the local government said on its website.
The Japanese man was in a stable condition in hospital, a spokesman for the festival said.
The four-minute run in Pamplona featured six bulls from the Jose Escolar ranch, one of which separated from the rest and caused panic among the runners.
The daily bull-run along an 825-metre stretch of narrow streets in Pamplona’s old town starts at 8 a.m. (0600 GMT) and usually lasts between three and five minutes. There are eight runs in total during the festival.
Over the past century 15 people have died in Pamplona’s event, which dates back hundreds of years, according to a count on the unofficial San Fermin website. The last death was recorded in 2009.