The court ruled that restrictions allowing only people with certain disabilities to vote at home must be lifted immediately.
The chairman of the court, Mykola Selivon, said all other provisions of the law were approved. He said he is confident that tomorrow's polling will produce a legitimate president.
Central Election Commission Chairman Yaroslav Davydovych said the rerun vote must be held as scheduled.
Representatives of both presidential candidates facing off in tomorrow's poll accepted the court's decision, saying the ruling will not affect the ballot's legitimacy.
Outgoing President Leonid Kuchma has accused both sides of putting personal interests ahead of the country.
Speaking today in a televized address, Kuchma said that it is up to every voter to choose the right path "towards a happy future."
"By choosing our new president next week, we are only beginning to choose Ukraine's path towards a happy future, which Ukrainian people have dreamed of," Kuchma said.
Kuchma said Ukrainians tomorrow must prove to themselves and to the world that they are freely and fairly choosing their new leader.
Voting at home and widespread use of absentee ballots were identified as the main sources of cheating in last month's election.
Supporters of opposition presidential candidate Viktor Yushchenko had pushed for the restrictions, saying they are necessary to prevent a repeat of the vote fraud that marred the 21 November presidential runoff.
Ukraine's Supreme Court anulled the results of that vote, canceling the victory of Prime Minister Viktor Yanukovych and ordering the new election on 26 December.
At the end of their respective campaign trails on 23 and 24 December, the two rivals in the election clashed over relations with the West. Yushchenko said Ukraine's strategic task is to seek integration with Europe. Yanukovych accused his political opponents of serving foreign groups trying to seize power. He said he was robbed of victory in the first election.
(compiled from wire reports)[For more RFE/RL coverage and analysis of the political crisis in Ukraine, click here.]