In all, 202 people died in the attacks, blamed on the al-Qaeda linked group Jemaah Islamiah.
At a memorial service in the beachside Sydney suburb of Coogee Ben Borgia, 27, delivered a heartfelt tribute to his sister Abbey, 13, and mother Debbie, 45 who both died in the blasts.
"I'd just like you to think for a second of all the things you have done since you were 13 years old - your first kiss, love, marriage, books, travel, choices, independence," he said.
"For the last four years I've had to learn to cope with the reality that the people I love most in the world aren't coming home from Bali."
Clutching single gerberas, the families and friends of victims and survivors gathered on the Dolphin Point headland at Coogee Beach, near the memorial to the 20 victims from Sydney's eastern suburbs.
Prime Minister John Howard offered his condolences in a statement, saying the sense of injustice and anger felt by the survivors and victims' loved ones would never subside.
"We owe it to the victims to succeed in the struggle against terrorism and extremism, and to re-emphasise the virtues of tolerance and harmony within our communities and our region," he said.
Perth services
In Perth, about 100 people gathered for a dawn service in Kings Park to remember the 15 West Australian victims.
Glen Brougham, who lost his 46-year-old sister Gerardine Buchan and her husband Steve in the Sari Club blast, said he still hoped justice would take its course.
"I would hate to see them get away with it, that would be the worst thing, but whether or not they're executed it's not for me to say. I'm not a violent thinking man," he said.
In South Australia, Premier Mike Rann called for October 12 to be made a national day of remembrance for Australian victims of terrorism - a proposal supported by acting New South Wales premier John Watkins.