The Social Democrats now have support of 33.0 percent of voters, according to the results of a poll carried out by the Synovate polling company and published on Thursday in the Dagens Nyhter (DN) newspaper.
The new figures put the Social Democrats, who suffered their worst electoral result in decades in Sweden's September 2010 parliamentary elections, back ahead of the Moderate Party, which registered support of 32.7 percent.
Since Håkan Juholt took over as head of party last month, support for the Social Democrats has climbed by 4 percent.
According to Synovate analyst Nicklas Källebring, however, it's still too early to attribute the poll results to some sort of "Juholt effect".
"It likely has more to do with the fact that a leaderless party now has a leader, which has allowed it to regain some of the voters it lost," he told DN.
But the Social Democrats' lead is small, just 0.3 percentage points. And the four parties of the governing centre-right Alliance coalition still have an overall advantage of 2.5 percent over the three main opposition parties.
In addition, all of the changes are within the statistical margin of error.
However, one result from the new poll which is statistically significant is a drop in support for the far-right Sweden Democrats from 6.2 percent to 4.2 percent.
"As soon as people start writing about them again, their support will increase. I see this as more of a temporary dip than a trend," said Källebring.
According to the poll results, support for the Moderates has dropped 4 percent since February.
Support for the Centre Party measures 4.7 percent, while support for the Christian Democrats came in at 3.8 percent, just below the 4 percent threshold for representation in the Riksdag.
The Liberal Party (Folkpartiet) saw its support increase by about one percentage point to 7.2 percent.
Support for the Left Party amounted to 4.1 percent, marking its worst poll results since 1994. Support for the Green Party, meanwhile, remained stable at 8.9 percent.