Chayaphon, 54-0 with 18 knockouts, will face 20-year-old Filipino southpaw Marco Rementizo, 12-3 with nine knockouts, in a 12-round mini-flyweight (105 pounds) matchup on April 25 at Fantasy Springs Resort Casino.
Chayaphon, also known as Wanheng Menayothin, is the longest-reigning active world champion, having taken his crown from Mexico’s Oswaldo Novoa with a ninth-round stoppage in November 2014.
Since then, the 34-year-old Thai fighter has won 18 consecutive bouts, defending the crown in 12 of them. His most recent triumph was a 12-round unanimous decision over South Africa’s Simphiwe Knonco in a title defense last October.
The fight is among four world title bouts on the undercard of a 12-round cruiserweight fight between Russian former light-heavyweight world champion Sergey Kovalev, 34-3 with one drawn and 29 knockouts, and Cuban former world title challenger Sullivan Barrera, 22-3 with 14 knockouts.
Nicaraguan twin brothers Felix and Rene Alvarado, both 31, will each defend a world title on the card.
Felix, 35-2 with 30 knockouts, will make the second defense of his International Boxing Federation light flyweight world title against South Africa’s DeeJay Kriel, 16-1-1 with eight knockouts.
Felix Alvarado won the vacant crown with a seventh-round stoppage of Filipino Randy Petalcorin in 2018 and defended for the first time last May with a unanimous decision over Japan’s Reiya Konishi.
Former IBF minimumweight champion Kriel, 24, has won eight fights in a row, most recently knocking out Mexico’s Jesus Aguirre last November.
Rene Alvarado, 32-8 with 21 knockouts, defends his World Boxing Association super featherweight title against Venezuela’s Roger Gutierrez, 24-3 with one drawn and 20 knockouts.
Brazil’s Patrick Teixeira, 31-1 with 22 knockouts, makes the first defense of his World Boxing Organization light middleweight crown against Argentina’s Brian Castano, 16-0 with one drawn and 12 knockouts.