A rabbi who taught at a Jewish Orthodox boys' school in Melbourne has pleaded guilty to child sex abuse dating back 20 years.

David Kramer, 52, pleaded guilty in the Melbourne Magistrates Court to six charges of indecent assault for the sexual abuse of students at the Jewish orthodox Yeshiva College in St Kilda East between 1990 and 1992.

It is believed Kramer is the first member of a Jewish institution to admit to child sex abuse allegations in Australia.

Kramer fled overseas in the early 1990s when accusations of abuse were raised with the college.

He was sentenced to seven years in jail in the United States for abusing a 12-year-old boy.

Kramer was extradited to face charges in Australia last year.

An advocate for the victims, Manny Waks, says it is an important milestone for the victims and a watershed for the Australian Jewish community.

"Today's conviction will send out a strong message to our community: you will be brought to justice irrespective of how far back you committed these crimes," he said in a statement.

"There is no immunity.

"Hopefully it will encourage some of his many other alleged victims to come forward."

He says the victims that he has spoken to are feeling anxious but relieved that justice has finally been served.

"We hope and trust that he will get the sentence he deserves," he said.

Kramer is due to return to court in July.