The Tymoshenko bloc is followed by the Party of Regions, led by the current premier, Viktor Yanukovych, and the pro-presidential bloc, Our Ukraine-People's Self-Defense, with 30.64% and 15.56% respectively, the commission said.
Other parties likely to overcome the 3% threshold include the Communists with 5.08% of the vote, former parliamentary Speaker Volodymyr Lytvyn's bloc with 4.17% and the Socialists with 3.19%.
The commission said turnout at Ukraine's second parliamentary elections since the 2004 'orange revolution' protests was 62.5%, with 50% required for the vote to be valid.
Preliminary results show the Tymoshenko bloc doing better than expected, and that it could form a governing coalition along with the bloc supporting President Viktor Yushchenko.
However, exit polls put Yanukovych's party, the 'orange' forces' rival, in the lead with 35.3%. Analysts have not ruled out protracted coalition talks, fresh political rows and rallies.
The president dismissed the legislature in April and called snap elections, accusing Yanukovych of "usurping power." The political rivals agreed on the September 30 vote following months of litigation and street rallies.