The researchers from the University of South Australia looked at the time children went to sleep and the time they got up, dividing children aged nine to 16 into four groups: early to bed, early to wake; early to bed, late to wake; late to bed, early to wake; and late to bed and late to wake.
They found those who went to bed earlier and woke up earlier were 1.5 times less likely to be obese than those who stayed up late and enjoyed a lie-in in the mornings.
To make the research fair, all the children studied had around the same amount of sleep - roughly nine and half a hours a night - and just slept and rose at different times.
The study found the children who went to bed early spent around 70 minutes a day being physically more active than those who stayed up late.
'We don't know if it's their sleep patterns that have knock-on effects to the kinds of activities they do or if their activities affect their sleep patterns,' said Carol Maher from the study.
'All we can say is it's clear from our study the kids who have that early to bed, early to wake up sleep pattern are doing better and are less likely to be overweight or obese.'