Two thirds of the 506 women aged 15 or more were overweight based on their height and weight (BMI), with four in ten (39 per cent) obese, according to the online survey carried out by global market research firm, TNS.
Two thirds were also trying to lose weight, primarily focusing on reducing the amount of fatty foods they eat, snacking less and exercising, said Tania Kullmann, TNS general manager.
But she added: "Worryingly, however, only 17 per cent of women undertake regular exercise - a symptom of not enough time in modern society for important priorities."
A quarter of the women surveyed were members of a slimming company, while 21 per cent were following an international weight-loss programme like the Atkins and South Beach diets and 22 per cent used weight loss pills.
Yet the study also confirmed the pressure on teenage girls to be thin. More than a quarter (26 per cent) of 15 to 19 year olds involved in the study considered themselves overweight when their BMI indicates they are not. Thirty per cent are in fact underweight.
"Being underweight is also unhealthy for our bodies," said Kullmann. "It is very concerning that almost one in three teenagers surveyed weigh too little. This points to growing levels of anorexia and bulimia."
The study was conducted by TNS throughout Australia in September using its online access panel, which has 325,000 active members. Based on the sample size TNS claims to be 95 per cent confident in the accuracy of the results which have a margin of error of +/- 4 per cent.