The woman hailed Miss Dominican Republic must relinquish her crown because she is married, beauty contest organisers say.
The rules state that those vying for the crown must be single. But Magaly Febles, director of the Miss Domincan Republic contest, said it had been discovered that Carlina Duran was married in 2009.
Contest organisers scheduled a news conference to give the crown to the first runner-up, 24-year-old Dulcita Lieggi.
Mrs Duran, 25, is from the town of La Vega, about 95 miles north of the nation's capital Santo Domingo, where she owns a spa. She has not commented publicly on the discovery of her true marital status.
She was crowned Miss Dominican Republic on April 17 and was to represent her country at the Miss Universe contest.
Ms Febles told the Dominican television news programme Noticias SIN that Mrs Duran acknowledged she was married.
Dominican newspaper Diario Libre said on its website that a marriage licence showed she was wed on June 6 2009.
In a statement read at a night news conference, Mrs Duran said she had never lived with her husband. "In my daily life, I remained like a single woman, without thinking of myself neither materially nor spiritually married," the statement, read by her lawyer, Radhames Cornielle, said.
The statement also said the marriage was brief and the couple had begun annulment proceedings.
Mrs Duran called her decision to hide her marriage from the contest organisers the "fruit of my inexperience".