S. Alexandra Burt and colleagues at Michigan State University also found that men with fewer nasty qualities were more likely to eventually end up married.
Among men who did marry, some showed signs that bad behaviour -- specifically traits associated with antisocial personality disorder such as criminal behaviour, lying, aggression and lack of remorse -- decreased after they tied the knot.
Burt said that married men "are just not as antisocial to begin with. And when they get married, they get even less antisocial."
In the study, presented in the December Archives of General Psychiatry, Burt and her colleagues followed 289 pairs of male twins for 12 years, from age 17 to age 29. More than half of the twins were identical.
Men who married during the study period, about 60 percent of them, showed less antisocial behaviour at ages 17 and 20, suggesting that men with more of these traits are less likely to get married in the first place.
By the age of 29, unmarried men had an average of 1.3 antisocial behaviours, compared with 0.8 among marrie men.
However, among identical twins in which one was married and one wasn't, the married twin had fewer antisocial behaviours after the union than the unmarried twin.
Given that identical twins, with similar genetics and childhood environments are likely to have the same antisocial tendencies, this indicates that marriage helped weed out those bad behaviours
It's not clear why men's behaviour might improve after marriage, said Ryan King at the University of Albany, State University of New York, who was not involved in the study.
Married men may spend more time with their spouses than their friends, and bad behaviour such as delinquency and binge drinking tend to be group activities, he noted.
In addition, married men "have more to lose" if they're caught doing illegal activities, and may care what their spouses think.
"Not everyone is equally likely to enter the institution of marriage, but those that do enter into it get some benefit from it," King said.
The results help explain consistent findings from other studies that men who are married commit fewer crimes. One recent study, for example, showed marriage was associated with a 35 percent reduction in crime.
Studies have also found that married people as a group tend to be healthier than singles, though recent research suggests the health advantage of marriage may be fading. But married people tend to live longer, be less depressed and suffer less from heart disease and stroke.