He also competed in the 1996 Olympics in Atlanta, Georgia where he lost to future record setting world champion Omar Andrés Narváez from Argentine.

After another second-round knockout win (this time at the Madison Square Garden in New York City), he returned to the Dominican Republic.

He later knocked out Hector Julio Avila in the second round on August 9, 2001, for the vacant NABO regional super bantamweight title.

Guzman added those two new regional championships and retained the one he already owned, by beating Edel Ruiz by decision, in a fight held in Tacoma, Washington on September 29, 2001.

Sánchez temporarily retired from boxing and Guzmán found himself fighting Fabio Oliva for the vacant WBO's world super bantamweight title on August 17, 2002.

Guzman then defended his new title with wins over contender Antonio Davis on December 18, 2006, and future two division champion Humberto Soto on November 17, 2007, both by unanimous decision.

In May 2008, Guzman elected to vacate his WBO super featherweight title in order to continue his career in the lightweight division.

[2] He was supposed to fight for Nate Campbell's unified WBA super, WBO and IBF titles, on September 13, 2008.

Guzman's well documented struggles to make the 135 lb lightweight limit prompted him to move to junior welterweight.

His first bout at 140 lbs against Jason Davis took place on the undercard of Amir Khan vs. Marcos Maidana on December 11 at the Mandalay Bay Resort & Casino in Las Vegas.

[9] After complying with an eight-month suspension for, admittedly, having used a diuretic in an attempt to make weight for his fight against Jason Davis in December, 2010; Joan Guzman returned to the ring at 140 lbs.

Guzman came in for the first official weigh-in a quarter-pound heavier than the mandatory 140 lbs., needing two more attempts to finally make weight.

Although Joan dominated all rounds, critics complained about his lack of 'killer instinct' and his showboating, which they say the ex-titlist might have used to hide the fact that he had grown physically tired.

On November 30, 2012, Guzman challenged Khabib Allakhverdiev for the IBO and vacant WBA super lightweight championship.

Guzman was knocked down in the third round, the result of a left; and blood readily flowing from the boxer's nose in the fifth set the momentum for the loss.