The tribunal, called the Extraordinary Chambers in the Courts of Cambodia, said in a statement that all the suspects were senior leaders.
The move comes about a year after Cambodian and foreign judicial officials took their tribunal posts.
Reams of evidence
On Wednesday, the tribunal announced that a detention facility at its headquarters, about 18 kilometers west of Phnom Penh, was ready to hold any defendants.
Prosecutors have submitted evidence including thousands of pages of documentation and the locations of more than 40 mass graves, the tribunal said in the statement.
Some two million people died from hunger, disease, overwork and execution as a result of the radical policies of the communist Khmer Rouge during its 1975-79 rule.
The late Khmer Rouge leader Pol Pot died in 1998 while his former military chief, Ta Mok, died in 2006.
The joint Cambodian-international team of prosecutors have submitted 25 cases involving "murder, torture, forcible transfer, unlawful detention, forced labor and religious, political and ethnic persecution", the tribunal said in the statement.
Trials were originally expected to start this year but bickering between Cambodian and foreign judges over procedural rules delayed the process.
Youk Chhang, director of the Documentation Center of Cambodia, an independent group collecting evidence of the regime's atrocities, said the list is a long-awaited "turning point of the tribunal".
"Things are moving along right now. There remains hope that justice will prevail," he added.