The protesters carried banners criticizing recent and planned increases in the prices of utility services and expressing support for the left-wing Center Party and People's Union, the two largest opposition forces.
While old Estonian folk songs filled the cold air, pensioners from all over the country arrived on buses paid for by the opposition parties.
The protest's organizers - the Estonian Pensioners Association, the Estonian Pensioners Union and the People's Union - said the three-party ruling coalition's pension policy does not serve pensioners' interests.
"The proportion of the average pension to average net wage has dropped from 45 percent in 1999 to 40 percent in 2000, and to below 37 percent in 2001, and it'll drop further as a result of the indexing of pensions in the coming years," said a written statement from the organizers.
The pensioners' organizations are also displeased because the government will channel a substantial part of the scant social insurance funds into obligatory pension insurance.
Estonian Social Affairs Minister Eiki Nestor said he went to the picket to find some concrete suggestions from pensioners on specific steps to reform the system.
"But nobody came up with specific ideas," he added.
"We Don't Need a Government Capable of Nothing! Set Pensions to 50% of Net Wages!" and "We Support the Pension Policy of the People's Union!" were a couple of the slogans protesters waved outside the Parliament.
But Nestor said it was impossible to make the pension half as much as the average salary, because it would require an additional 1.7 billion kroons ($97.14 million) from the state budget. As a practice run for the Nov. 20 mass rally, local pensioners' organizations staged meetings and pickets in nine regional capitals the day before.