Robert Andrew Fiddes Ellis was found guilty of abusing at least 11 girls since 2014 at his home on the island. The 70-year-old would bathe the children -- aged between seven and 17 -- and touch them inappropriately, prosecutors said.
"His actions could have damaged the victim's futures," said judge Wayan Sukanila, as he announced a guilty verdict and handed down the 15-year sentence at a court in the Balinese capital Denpasar.
His actions "could also damage the image of Indonesia, and Bali in particular, for tourists," he added.
His defence team claimed he had only bathed the children and never intended to molest them.
Ellis, who has long, white hair and a big bushy beard, looked sad when the verdict was announced and his lawyer said he would file an appeal as police had treated him in an "inhumane" manner.
Authorities had only focused their investigation on Ellis when two other people involved in bringing him the children had yet to be questioned, said lawyer Yanuar Nahak.
At an earlier hearing, Ellis had admitted his actions but tried to downplay them, telling reporters: "I did it -- but it's not a serious thing."
In addition to the jail sentence, Ellis was ordered to pay a fine of two billion rupiah (around $153,000) or serve an additional six months in jail.
Bali is a popular holiday destination for tourists from around the world, who flock to the island for its beaches, resorts and nightlife.
Ellis is not the first person to be jailed for child sex offences. In 2009, 61-year-old Australian Philippe Robert Grandfield was sentenced to eight years prison for paying underage boys for sexual favours.
Robert Andrew Fiddes Ellis of Australia attens his trial inside a court room in Denpasar on Bali island.
An elderly Australian man was jailed for 15 years Tuesday for sexually abusing Indonesian girls on the resort island of Bali after luring them to his house with promises of gifts.
