Japan's lower house of parliament has passed controversial legislation to privatise the country's postal system.
Mr Koizumi says the reforms are crucial to stimulate economic growth
The legislation will now go to the upper house, where a vote is expected to be held within the next few days.
Prime Minister Junichiro Koizumi has made privatisation of Japan Post the cornerstone of his economic reforms.
It was parliament's rejection of the plan in August which prompted Mr Koizumi to call a snap election last month, which he won with a landslide.
According to the BBC correspondent in Tokyo, Chris Hogg, it is fair to say that Mr Koizumi is obsessed with privatising Japan Post.
When rebels in his own party helped to block his plans earlier this year, he called a general election as referendum on his reform agenda.
JAPAN POST IN NUMBERS
Manages 25% of Japan's personal assets
25,000 offices and 260,000 employees
330 trillion yen (nearly $3 trillion) in savings and deposits
85% of population has postal savings
His gamble paid off and his coalition won more than a two-thirds majority. His first act back in power was to reintroduce the bills into parliament.
The bills will now go to the upper house, where they were voted down earlier this year.
Several former rebels there have said they will now support Mr Koizumi's plans.
And even if the bills were to be rejected again, the prime minister now has enough votes in the Lower House to overturn that decision.
On this issue, Mr Koizumi now cannot lose, our correspondent says.
State-owned Japan Post runs a savings bank with more than $3 trillion (£1.7 trillion) in assets, making it possibly the largest financial institution in the world.
It runs nearly 25,000 post offices and employs some 400,000 workers.
Under Mr Koizumi's plan, the postal system would be fully private by 2017.
The process is expected to start in 2007, but political wrangling has forced the government to delay the launch for six months, and possibly into 2008.
Analysts say the prime minister sees the reforms as essential to stimulate growth and open up government-dominated sectors to greater competition.
"Postal privatisation is very important for Japan and it is an issue that we cannot avoid," said Economics Minister Heizo Takenaka, who is in charge of implementing the changes.
As well as making clear his determination to press ahead with postal reform, Mr Koizumi has also hinted at further privatisation.