Serrano, owner of long arms and a sturdy chin, began his career on October 29, 1969 with a four round decision win over Ramon Laureano. He built a fan base in Puerto Rico, campaigning there for his first 23 bouts, including winning and losing the Puerto Rican Featherweight title v.s Francisco Villegas. For his 24th bout, he travelled to Panama City, where he met future world Featherweight champion Ernesto Marcel, who beat him on points in 10 rounds. That would be his last defeat in a long time.
He then continued his winning ways, including a 10 round decision win over tough veteran Cocoa Perez and one win over former title challenger Diego Alcala, also by decision in 10. Serrano then travelled in 1976 to Honolulu, Hawaii, to meet reigning WBA world jr. Lightweight champion, the Filipino Ben Villaflor. Serrano outboxed Villaflor, but was the victim of a terrible decision and had to return home only with a 15 round draw.
The WBA ordered an immediate rematch, and so on October 16 of the same year, Villaflor went to San Juan to defend his title for the second time vs. Serrano. Serrano, more furious than the first time around, outboxed Villaflor and used his ring technique to win 12 of the 15 rounds on each judges' scorecards. As life had it, Samuel Serrano was destined to become a world champion in front of his fans.
Serrano became a great champion, defending his title in places like Venezuela, Ecuador, South Africa, Japan (twice) and, of course, Puerto Rico. One of his defenses, against Julio Diablito Valdez, resulted in a after-fight brawl when Serrano was announced as winner by a unanimous decision and went to greet his rival but was received with a punch to the face. Serrano retaliated, and police intervention was needed. Both fighters were escorted to their dressing rooms by the police. But disaster struck in Detroit on August 2 of 1980, when, after leading on all scorecards, he was struck by a Yasutsune Uehara right hand to the chin in round six, and lost his title by knockout to the Japanese. After that loss, he set his eyes on recovering his world title from the Japanese world champion, and so on April 9, 1981, they met again, this time in Wakayama, Japan. Serrano was more cautious this time, and didn't try to go for the knockout after building a points lead. Uehara was given such a boxing lesson that, even in his homeland, all judges agreed and gave Serrano the world title back by a unanimous decision.
Serrano made two defenses and then went to Chile to give challenger Benedicto Villablanca a chance at the title on June 3rd, 1982. It proved to be a highly controversial fight. After 5 rounds, Serrano was ahead on the scorecards. However, a cut appeared over his eye during the 6th, and the referee ruled it to be from a punch. Serrano kept outboxing his foe, but during the 11th round, the cut was so deep, the fight had to be stopped by the doctor and Serrano had to be taken to a Santiagohospitalhospital. Since the referee ruled the cut came from a punch, initially the fight and the world title were given to Villablanca.
Serrano and his corner filed a complain, however, claiming the cut had been caused by a headbutt instead, and upon review at the WBA's Panama City offices, WBA officials announced they had effectively seen the headbutt that Serrano claimed opened his cut happen. So the WBA decided the cut had come from a headbutt, and the judges' scorecards were reviewed. They had Serrano ahead on points after 10 rounds, so the fight, and the crown, were given back to Serrano.
In his next defense he met the younger and pshysically stronger Roger Mayweather. Serrano and Mayweather gave it a good fight for most of 7 rounds, but Serrano was weakened by a barrage towards the end of the 7th, and downed with a right hand in the 8th, this time, losing the title definitively.
During his time retired, he tried such business ventures as a sports shop, a record store and a gym. He lived in one of the most impressive mansions in Bayamon, Puerto Rico. But he was also being introduced to the underworld, and in 1987, he was convicted to 15 years of jail on charges of drug trafficking.
He came out in 1995, and made a short return to the ring, winning the Puerto Rican Lightweight title vs Sammy Mejias on a 12 round decision in 1996 and winning a 10 round decision vs Anthony Ivory in 1997.
He retired after the Ivory fight.
He retired with a final record of 51 wins, 4 defeats and 17 knockouts, and is now working as an eletrician for the Puerto Rico Telephone company.
Serrano enjoys his celebrity and loves signing autographs for fans at public appearances. He has steered clear of trouble for the last 8 years.