The Red-Green coalition now has a lead of 5.1 percentage points over the centre-right Alliance parties that made up the previous government under Fredrik Reinfeldt, according to a survey by pollsters Demoskop.
It concluded that 44.4 percent of the population would vote for the current coalition parties if there was another election.
The Sweden Democrats have also seen a rise in support, with 13.3 percent of those surveyed suggesting that the nationalist group was their preferred party.
"SD's growth is from a dissatisfaction with immigration policy where the other seven parties agree," Peter Santesson, head of the public opinion analysis on Demoskop told news agency TT.
The Feminist Initiative saw the biggest decline of all parties, with a 1.0 percentage point drop.