Joseph "JoJo" Pedroza Diaz Jr. (born November 23, 1992) is a Mexican-American professional boxer who held the International Boxing Federation (IBF) super featherweight title from 2020 to 2021.

Joseph is of Mexican descent. He attended Kranz Intermediate at the age of 12–14. He is left-handed and fights southpaw. As a child he played baseball but took up boxing to learn self-defense. He is coached by his father. He attended South El Monte High School.

Prior to the Olympic Trials, he was the two-time reigning national champion at bantamweight that included a win over Antonio Nieves. Diaz became the first American boxer to qualify for the 2012 Olympics by becoming a quarter-finalist at the 2011 World Championships, where he defeated both 2004 Olympic silver medalist Worapoj Petchkoom of Thailand and former world championship bronze medalist Óscar Valdez of Mexico but lost to Lázaro Álvarez. Díaz was the 2011 U.S. National Champion at featherweight at the U.S. Olympic Training Center in Colorado Springs, Colorado. He fought in the 2010-11 World Series of Boxing

At the 2012 Summer Olympics he beat Pavlo Ishchenko, but ran into Alvarez in his second fight and lost again.

Diaz made his professional debut in 2012 against Vincent Alfaro, winning by unanimous decision over four rounds and also scored a knockdown in the fourth. On May 9, 2015, Diaz defeated Giovanni Delgado via unanimous decision on the undercard of the Canelo Álvarez vs James Kirkland fight. He stepped up competition against veteran Rene Alvarado in a fight televised on HBO Latino in July 2015 and on December 18, Diaz Jr. defeated Hugo Partida and earned the WBC-NABF featherweight title. He went on to defend the title multiple times, before challenging Gary Russell Jr. for the WBC featherweight title on May 19, 2018, at the MGM National Harbor in Oxon Hill, Maryland. Diaz was unsuccessful, losing a unanimous decision to scores of 117–111, 117–111, 115–113.

On January 30, 2020, Diaz defeated IBF super featherweight champion Tevin Farmer by unanimous decision with scores of 115–113, 115–113, and 116–112 to claim his first world title. After the fight, Diaz praised his opponent, saying "Tevin Farmer is a hell of a fighter, guys. I thank him for giving me this opportunity."

Diaz's first defense of his IBF super featherweight title was scheduled for February 13, 2021 against Shavkat Rakhimov. However, he was stripped of the title when he missed weight, weighing 3.6 lbs over the 130 lb limit. As a result, the fight still went ahead, but Diaz was fined $100,000 for missing weight, which represented 20% of his purse. The money was split evenly between Rakhimov and the California State Athletic Commission. They fought to a majority draw, with scores of 115–113 Diaz, 114–114, 114–114.

Following his draw with Shavkat Rakhimov, Diaz moved up to the lightweight division which he promised would be his best weight, where he fought Javier Fortuna for the vacant WBC interim lightweight title on July 9, 2021. Diaz was docked a point in the fourth round for hitting behind the head, but nonetheless emerged as the victor via unanimous decision, with scores of 117–110, 116–111 and 115–112.