A team from the Institute of Psychiatry analysed data from former US soldiers who served during the Vietnam war era.
They found that those who performed better on intelligence tests tended to have more that was also more mobile sperm.
The study in the journal Intelligence, appears to support the idea that genes underlying intelligence may have other biological effects too. Therefore, if tiny mutations impair intelligence, they might also harm other characteristics, such as sperm quality.
Supporting the theory, people with robust genes might be blessed with a biological "fitness factor" making them fit, healthy and smart.
Previously it was assumed that lifestyle factors were more likely to be cause of any relationship between intelligence and health.
Examples such as, brighter people may be less likely to smoke, and more likely to take exercise, both of which are known to impact on mental performance.
The latest study tested the gene theory by taking two characteristics that seemed unlikely to be associated with each other - intelligence and sperm quality.
They found a small, but statistically significant link, and were able to show that this could not be explained by unhealthy habits, such as smoking or drinking alcohol.
The researchers found that independently of age and lifestyle, intelligence was correlated with all three measures of sperm quality - numbers, concentration, and ability to move.
Though caution should be taken when forming conclusions with the results as the improvement in semen quality with intelligence observed in this paper are small and therefore it is unlikely to have a big impact on the ability of men of different intelligences to conceive.
The semen samples were collected in 1985 by the US Centers for Disease Control as part of a large-scale study into the health of US soldiers who served during the Vietnam Era. Some of the men in the sample had served in Vietnam, some had served in Germany, Korea and the USA.