Saudi Arabia has started issuing new marriage contracts that require the age of the bride to be given, in an attempt to stop underage girls from marrying.
The kingdom had promised new measures after a series of high-profile cases involving young brides.
Human rights groups have welcomed the new measures, saying clear-cut rules were needed to ensure underage girls were not harmed.
Saudi Arabia has no law against child marriage.
"There is a serious drive by the [justice] ministry to determine an age for girls to marry following the recent reporting of older men marrying young girls," an official told the Saudi-based Arab News newspaper.
The National Society for Human Rights welcomed the new measures.
"The marriage of underage girls has been in the limelight for the past three years," said NSHR chairman Mufleh Al-Qahtani.
"A number of lawsuits have also been filed to stop fathers marrying off their underage girls to older men."
In February a 12-year-old girl decided to stay married to an 80-year-old man, after initially filing for divorce.
A $22,600 (£14,174) dowry had been paid to her father just months before.
In 2008, the case of an eight-year-old girl who was married to a 50-year-old man was revealed when the child's mother tried to annul the marriage.
Defenders of child marriage say the practice is part of Saudi culture.