People who down four cups a day can see their risk of developing a tumour drop by about 15 per cent.
But those who got through six or more were up to 40 per cent less likely to fall victim to the disease.
Tea lovers, however, did not see any reduction in risk, scientists said.
More than 40,000 people a year in the UK are diagnosed with bowel cancer.
The disease has a high mortality rate - around 16,000 a year - because many victims ignore early warning signs and only seek medical help once the cancer has advanced.
Consult your GP about coffee drinking first
Diets high in fat and red meat, as well as lack of exercise, are thought to be among the main risk factors.
Some previous studies have hinted coffee could have a protective effect, although the findings have been inconclusive.
In the latest investigation, researchers at the US National Cancer Institute in Rockville, Maryland, looked at nearly 490,000 men and women who took part in a diet and health study from the mid-nineties onwards.
They analysed their eating and drinking habits and compared bowel cancer rates among coffee drinkers and non-drinkers.
The results, published in the latest American Journal of Clinical Nutrition, showed a small but significant fall in tumour risk among those on four to five cups a day.
But the greatest benefits were seen when consumption topped half-a-dozen cups a day, with the risk plummeting by almost 40 per cent for certain types of tumour.
Previous studies have suggested five cups of coffee or tea every day could slash the risk of a brain tumour by around 40 per cent.
And Japanese scientists found just one cup a day could nearly halve the risk of dangerous cancers affecting the mouth and gullet.
Dr Euan Paul, executive director of the British Coffee Association, said: “It is particularly encouraging to see that coffee consumption may lower the risk of bowel cancer given that over 40,000 men and women are diagnosed with it in the UK every year, making it the third most common cancer.”
But he stressed that pregnant women should followed NHS advice to moderate their intake of caffeine to 200mg per day from all sources, as it can increase the risk of miscarriage in high doses.
Mark Flannagan (CORR two Ns), chief executive of the charity Beating Bowel Cancer, said” “As always with such studies, it is likely further research will be needed before we can give any clear advice about caffeine intake and reduced bowel cancer risk.
“However, people can take immediate steps to reduce their risk of developing bowel cancer, the UK’s second biggest cancer killer, by making simple changes to their lifestyle and diet.
“Anyone looking to lower their risk of developing bowel cancer should reduce their intake of red and processed meat, high fat foods and alcohol, and increase their intake of fruit, vegetables and fibre, take regular moderate exercise and stopping smoking.
“In the case of coffee consumption we recommend that you consult your GP first.”
This is the latest research to hail the benefits of coffee.
It has been shown to reduce the risk of Parkinson’s, Alzheimer’s disease, stroke, diabetes and breast cancer.