The research on more than 200,000 women from nine European countries found doing household chores was far more cancer protective than playing sport.
Dusting, mopping and vacuuming was also better than having a physical job.
The women in the Cancer Research UK-funded study spent an average of 16 to 17 hours a week cooking, cleaning and doing the washing.
Experts have long known that physical exercise can reduce the risk of breast cancer, probably through hormonal and metabolic changes.
But it has been less clear how much and what types of exercise are necessary for this risk reduction.
And much of past work has examined the link between exercise and breast cancer in post-menopausal women only.
The latest study looked at both pre- and post-menopausal women and a range of activities, including work, leisure and housework.
All forms of physical activity combined reduced the breast cancer risk in post-menopausal women, but had no obvious effect in pre-menopausal women.
Out of all of the activities, only housework significantly reduced the risk of both pre- and post-menopausal women getting the disease.
Housework cut breast cancer risk by 30% among the pre-menopausal women and 20% among the post-menopausal women.
The women were studied over an average of 6.4 years, during which time there were 3,423 cases of breast cancer.
The international authors said their results suggested that moderate forms of physical activity, such as housework, may be more important than less frequent but more intense recreational physical activity in reducing breast cancer risk.
Dr Lesley Walker of Cancer Research UK said: "We already know that women who keep a healthy weight are less likely to develop breast cancer.
"This study suggests that being physically active may also help reduce the risk and that something as simple and cheap as doing the housework can help."
He recommend that men and women take regular exercise and maintain a healthy body weight to help prevent cancer.
The research is published in the journal Cancer Epidemiology Biomarkers and Prevention.