Sharon resigned from Likud less than two weeks ago after concluding that his energies would be sapped by rebels who opposed his Gaza Strip withdrawal and would try to block further territorial concessions to the Palestinians. Since then, polls show his new, centrist Kadima party steadily gaining and Likud steadily shrinking.
The Labour Party, led by its charismatic new leader, union boss Amir Peretz, held firm from previous surveys at 26 seats.
The poll of 500 people, conducted by the Dialogue survey institute, did not give a margin of error. It was conducted before Labour stalwart Shimon Peres announced on Wednesday night that he was quitting Labour to team up with Sharon.
Likud, whose hard-line policies dominated Israeli politics for nearly three decades, is to choose a new leader to replace Sharon in 19 December primaries.
Over 37% of the Likud voters polled said Defence Minister Shaul Mofaz would bring the party the most seats in parliament, while 34% said former prime minister Benjamin Netanyahu, who favors a tough line against the Palestinians, would.