The Australian Bureau of Statistics (ABS) said people were continuing to pile on the kilos despite other findings indicating a switch to healthier habits.
The study found 63.4 percent of the population are now classified as overweight or obese -- an increase of more than two percent from four years ago.
"The proportion of overweight adult Australians has increased by more than two percentage points, meaning that nearly two-thirds of the population are now classified as overweight or obese," said ABS statistician Paul Jelfs.
The figure compares to 56.3 percent in 1995 and 61.2 percent in 2007-08.
Jelfs said the 2011-12 Australian Health Survey of 33,500 people found that 70.3 percent of men and 56.2 percent of women were losing what he called the "battle of the bulge", with one-quarter of children also classed as overweight.
The survey, described by ABS as the "largest check-up on the nation's health ever undertaken", calculated whether or not people were too heavy using the Body Mass Index system.
The formula for calculating a person's BMI is weight in kilograms divided by height in metres squared. The resulting number then tells researchers whether the individual is overweight for their height.
Australia is ranked fifth among advanced nations in terms of obesity after the United States, Mexico, New Zealand and Chile, according to the OECD.
Despite the worrying trend for increasing obesity, Jelfs said the survey did throw up some heartening findings.
The number of daily smokers fell three percent in the past four years, to 16.3 percent, or 2.8 million smokers, out of a population of nearly 23 million.
The rate was 18.9 percent in the 2007-08 survey and 22.4 percent back in 2001.
Australia won a High Court battle with major cigarette firms this year to become the first country in the world to mandate plain packaging for tobacco products in a bid to curb smoking and related health costs.
It is also trying to reduce binge-drinking through a combination of shock advertising campaigns and taxation, with a government report due to be released in coming weeks on the potential introduction of a floor price on alcohol.