The Australian Bureau of Statistics report into national social trends said 54 percent of adults were excessively overweight based on 2004-05 figures, up from 45 percent in 1995.
"It has been estimated that obesity and its associated illnesses cost Australian society and governments a total of 21 billion dollars (18 billion US) in 2005," the bureau said.
It said the most striking increase in obesity was among men aged 35-44, which almost doubled in the decade to 2004-05.
The bureau said health problems related to obesity were also on the rise, with 3.6 percent of the adult population suffering from diabetes in 2004-05, compared with 2.4 percent in 1995.
The statistics also show Australians are becoming less likely to marry, revealing that 31 percent of currently single men and 26 percent of women would never tie the knot.
For those who do get married, the divorce rate increased from 28 percent to 33 percent, with one in five children in one-parent families.
However, the country's fertility rate ticked up to 1.81 babies per woman in 2005 after hitting an all-time low of 1.73 in 2001.
The figures revealed that Aborigines remain one of Australia's most disadvantaged groups, more than three times as likely as non-indigenous people to have diabetes and more than 10 times as likely to have kidney disease.