But the researchers also found that beards could make men look more formidable to other men who might compete with them for a woman's attention.
Writing in the Journal of Evolutionary Biology, Dr Barnaby Dixson, a psychologist at the University of Queensland in Australia, and his colleagues said: 'Our findings suggest that beardedness may be attractive when judging long-term relationships as a signal of intrasexual formidability and the potential to provide direct benefits to females.
"Relationship context also had effects on ratings, with facial hair enhancing long-term, and not short-term, attractiveness."
Many previous studies have found that masculine faces are often perceived as being more attractive to the opposite sex for short term relationships than those that are more feminine.
Those with more feminine features, such as soft jaw lines, smaller noses and fuller lips, tend to be seen as a better choice for long term partners.
However, while past fashion trends and the rise of metrosexuals saw men emphasising their feminine features, more recently there has been a shift back to men having facial hair.
The researchers used computer graphic manipulation to morph a series of male faces from clean-shaven, light stubble, heavy stubble and full beards.
They also altered features like the brow ridge, cheekbones and jaw line to make the face appear more or less masculine.
When women viewed the images, they found that a beard appears to help make a man's face look more reliable for a long term relationship even if they have masculine features.
This may be due to cultural associations where beards have become a sign of maturity and wisdom.
Dr Dixson and his colleagues said there appears to be a trade-off between masculine facial features and growing a beard.
They said: "Male-typical facial features such as a pronounced brow ridge and a more robust jawline may signal underlying health, whereas beards may signal men's age and masculine social dominance.
"However, masculine faces are judged as more attractive for short-term relationships over less masculine faces, whereas beards are judged as more attractive than clean-shaven faces for long-term relationships
"Our results hint at a divergence of signalling function, which may result in a subtle trade-off in women's preferences."