The anti-immigration Sweden Democrats scored 18.9 percent, the largest figure they have got so far in a poll by Ipsos.
Meanwhile the poll, commissioned by Swedish newspaper Dagens Nyheter, suggested that the ruling coalition parties, the Social Democrats and the Greens had lost the support of around half a million Swedish voters and would score just 37.3 percent of the vote if there was an election now.
According to analysts at Ipsos, support for the country's opposition centre-right Alliance parties has barely shifted, with around 41.3 percent of voters likely to choose them.
The polling was carried out between December 3rd and December 14th, after the Swedish government announced a shock tightening of asylum rules in a bid to stem the influx of refugees to the Nordic nation.
The move has led to a fall in the number of people registered by Sweden's Migration Agency (Migrationsverket). While in October around 10,000 people were registered in a week, Migrationsverket statistics suggest that 4,721 people sought asylum across Sweden during the first seven days of December.
Tommy Möller, a professor of political science at Stockholm University, told the TT news agency that the results bucked the common trend of voters increasing their support for a ruling government during a national crisis.
"Some of the voters seem to think that while Sweden has a refugee crisis, the government itself created it by attracting refugees," he said.
The expert noted that the Sweden Democrats had managed to gain votes, despite "the other parties now effectively approaching their standpoint".
A second poll released on Thursday, using slightly different methodology, suggested even greater support for Sweden's far-right.
The research for pollsters Novus for Swedish broadcaster TV4 indicated that 22 percent of voters would choose the nationalist Sweden Democrats if there was an election.