On March 28, 1997, Wonjongkam knocked out Mzukisi Sikali of South Africa in 48 seconds to win the WBU Light Flyweight Championship.

[5] On November 17, 2006, Wonjongkam defeated South African boxer Monelisi Mhikiza Myekeni by unanimous decision.

Wonjongkam suffered a shocking upset decision loss to Daisuke Naito in July, 2007, ending his long run as champion.

Wonjongkam won the vacant Interim WBC Flyweight Championship in a bout against Mexican Julio César Miranda on April 24, 2009.

On March 2, 2012, Wonjongkam lost his Lineal, The Ring and WBC Flyweight Titles in an upset technical knockout stoppage to Sonny Boy Jaro of Philippines.

Wonjongkam won the vacant WBC International flyweight title against Hyobu Nakagama on August 31, 2012.

However, he lost the title to Rey Megrino on November 1, 2012, by a third-round TKO, marking Wonjongkam's fifth defeat.