A 10-year study of 5,275 men with the early stages of disease, conducted by the Texas Southwestern Medical School in Dallas, US, found that aspirin reduced the risk of dying from 10 per cent to four per cent.
They discovered that patients with tumours which had not spread beyond the prostate gland, and who were also being treated with surgery or radiation, saw a drastic improvement in their life expectancy by taking the drug.
Aspirin was found to have a positive effect on all patients - but those with more aggressive forms of the disease appeared to get the most benefit, reports the Daily Mail.
These findings will be presented at the American Society for Radiation Oncology in San Diego, US.
Previous trials have suggested prostate cancer may be prevented by daily doses of aspirin but there have been mixed results.
The findings come a week after a study found that healthy people can cut their risk of bowel cancer by taking 75 mg of aspirin daily for five years.
And earlier this year, US researchers said the painkiller could help women with breast cancer.
Of the 5,275 men taking part in the study, 1,982 were taking anticoagulant drugs such as aspirin and warfarin - usually for other conditions such as heart disease.
As a result there were varying doses of anticoagulants being taken. The anti-cancer effect was found with all such drugs but was "most prominent" with aspirin.
The risk of prostate cancer spreading to the bones was also cut, along with the risk of dying from the disease.