Koizumi did not provide details of the bill or when it would be submitted, but he said the proposal would be in line with the findings of a high-level panel, which has recommended letting female heirs lead the world's oldest hereditary monarchy.
Japan's imperial family has not produced a male heir since the 1960s, and public opinion is strongly in favor of changing a 1947 law to allow Crown Prince Naruhito's four-year-old daughter, Aiko, to become a reigning empress. Aiko is his only child.
"In order that the imperial throne be continued into the future in a stable manner, the government will submit a bill to reform the Imperial Household Law," Koizumi said in a major policy speech at this year's opening session of parliament.
Under the Imperial Household Law, only males who have emperors on their father's side can succeed to the throne. The last woman to take the crown was Gosakuramachi, who reigned from 1762 to 1770. Only seven other women have had the honor.
The idea has gained strength in recent years as the imperial family, which is deeply respected in Japan, has faced the growing possibility of a succession crisis.
As Emperor Akihito's eldest son, Naruhito is next in line to the throne. But he and Crown Princess Masako have not had a son; neither have Naruhito's younger brother Prince Akishino and his wife Princess Kiko.
The prospects of a male heir emerging dimmed even further when Masako dropped out of public view two years ago because of a nervous illness. She has appeared in public only sporadically since then, and skips many imperial events.
The idea of a woman on the throne has wide public support, but it has caused a considerable stir in Japan's hidebound imperial circles and among conservatives.
"I think it is way too hasty," said Akira Momochi, an expert on the imperial family at Nihon University. "The imperial succession of male heirs is a tradition of 2000 years. It is unthinkable that a group of people that are not even experts in this area have reached a conclusion on a fundamental change of this basic right."
The prospect of such a change even prompted Prince Tomohito, a cousin of Emperor Akihito, to write an essay suggesting a revival of the long-discontinued practice of employing concubines to produce male heirs.
The prince, who is fifth in line to the throne, also suggested emperors be allowed to adopt sons and the aristocracy, disbanded after World War II, be reinstated to create a larger pool of marriage partners and potential heirs.
Those ideas, however, are not being taken seriously by the public and harken to an era far in the past.
Though the late Emperor Hirohito resisted pressure to take a concubine himself, both his father, Emperor Taisho, and his grandfather, Emperor Meiji, were the sons of concubines. Akihito is Hirohito's only son.
Under the recommendations of an independent panel late last year, the law would be changed to give the emperor's first-born child of either sex the right to head the monarchy.
The proposal is overwhelmingly popular in Japan. In three separate polls taken in December, by the Mainichi and Yomiuri newspapers and Kyodo News Agency, more than 70 percent of respondents said they support placing a female monarch on the throne.