The accident took place overnight in northeastern Kratie province, some 160km northeast of the capital Phnom Penh, Major Leng Sarum of the police said on Sunday.
Thirty passengers had been on the boat that was on its way to a Buddhist festival.
"There was no storm or heavy rain when the boat sank. The accident happened because it was overloaded with passengers," Sarum said.
Kham Phoeun, the governor of Kratie province, said the bodies of 17 dead, which included 14 women and two children under the age 5, were being given to relatives.