"We have taken back millions of US dollars," Trong told a packed conference room. "We will persevere with the fight against corruption."
During his second term in office, Trong presided over a "blazing furnace" anti-corruption campaign that saw numerous high-ranking officials arrested and two members of the politburo expelled from the party. One is now in prison.
His comments came shortly after the party ended its final session of the congress amid much fanfare and repeated exclamations of "great success!" and "glory to the Socialist Republic of Vietnam!"
On Sunday, the party announced its new party chief and 18-member politburo for the next five years.
76-year-old Trong, incumbent general secretary of Vietnam's Communist Party, will hold his post for a third term, with a new resolution adopted to allow someone of his age to remain in power.
Trong’s reappointment means his reign as party chief is now the longest since Le Duan took control following the death of revolutionary leader Ho Chi Minh in 1969.
The congress ended a day early as the country battles a raging Covid-19 outbreak, with 240 cases confirmed since two clusters emerged in northern Vietnam on Thursday.
Bars, karaoke parlours and schools in Hanoi have all been closed as of Monday after the virus re-emerged in the Vietnamese capital for the first time in six months.
Vietnam has officially confirmed 1,819 coronavirus cases, along with 35 deaths. - dpa