Foreign Secretary James Cleverly said getting the private sector on board was the aim of the two-day Ukraine Recovery Conference that starts in London on Wednesday.
He hosted US Secretary of State Antony Blinken on the eve of the summit, who said Washington would announce a new assistance package for Ukraine this week.
The cost of reconstruction after Russia's invasion has been estimated at more than $400 billion by the UN and the World Bank.
The 16-month conflict has destroyed homes, schools and hospitals, forcing millions of women and children to flee. Ukraine has also been told it must address concerns around corruption if it hopes to one day join the European Union.
"This week is very much about encouraging the private sector to invest in Ukraine’s rebuilding and recovery," Mr Cleverly said.
"That means that we need to demonstrate that those investments will be effective and that they will be safe. That of course means the ongoing assurance that the Ukrainians seek that they will not be re-invaded once they have successfully regained their territory.
"But of course, it also means supporting them as they perform the reform of their institutions that will facilitate the investment in their country."
Kyiv is seeking Nato membership or alternatively guarantees from western powers that they would step in if Ukraine is attacked again once the war ends.
Ukraine's President Volodymyr Zelenskyy is expected to address the London conference by video link.
Mr Cleverly said the "swift transformation" of Ukraine's Soviet-derived military into a Nato-backed force able to resist Russia was a model for civilian institutions.
"We want to see that same alacrity and pace with the reform of their governmental institutions," he added.
He said a significant part of the post-war costs should be extracted from Russia under the principle of "you break it, you bought it".
Mr Blinken, who with Mr Cleverly visited a Ukrainian church in London, said he would announce a "new robust US assistance package" on Wednesday.
He said the US aim was to "build a military for the long term" in Ukraine so that it could deter or repel future aggression.
However, he would not be drawn on whether the US would provide longer-range ATACMS missiles as Ukraine has sought.
The "flip side" of military aid is building "the strongest possible economy, the strongest possible democracy, which is actually necessary to achieve a thriving economy and for reconstruction", Mr Blinken said.
"If Ukraine is going to attract the investment that it’s going to need, not just from governments, not just from international financial institutions but from the private sector, it has to build the best possible environment to attract that investment."