Many at the rally wore white scarves and armbands as they waved opposition flags in front of the Georgian parliament building, using the colour and symbols of last year's violently dispersed anti-government protests.
Valery Kutsia, a retired policeman at the rally, said:"I'm here to protest because there is no justice in Georgia. Human rights are not respected. We must have early elections."
One banner read "Stop Russia, Stop Misha", reflecting the protesters' opposition to both Russia and Saakashvili, who has the nickname Misha.
Though Saakashvili was praised in the West when he came to power in a non-violent "Rose Revolution", he has been criticised since the August war for acting recklessly.
Opponents also accuse him of persecuting opposition activists, limiting media freedoms and ignoring the poor in his drive to implement economic reforms.
Dato Darchiashvili, a member of parliament from Saakashvilis' party, told Al Jazeera the media restrictions had been carried out last year to prevent the country being destabilised.
Matthew Collin, Al Jazeera's correspondent in Tbilisi, the Georgian capital, said: "President Saakashvili says he's now learned his lessons and he's promised new democratic reforms.
"But Georgia's radical opposition parties who have gathered outside parliament have ignored his calls for post-war unity. They simply want him to go."
On the eve of Friday's demonstration, a coalition of opposition parties distributed a pamphlet laying out plans for a number of rallies and other actions designed to pressure the government into calling elections by next spring.
If Saakashvili has not called elections by April 9, the anniversary of a 1989 Soviet crackdown on protesters that left 20 dead, the opposition will begin a "round the-clock" protest rally, it said.
In August, Russian forces moved into the country to counter a Georgian military attempt to retake the separatist region of South Ossetia.
Russia's military defeated Georgian forces, occupied parts of the country and bombed targets across Georgia, badly damaging the country's infrastructure.
Under a European Union-brokered ceasefire, Russian forces later withdrew to South Ossetia and another separatist region, Abkhazia.
|Russian forces inflicted heavy damage to Georgia's infrastructure [AFP]
Analysts say the protest will be a first sign of whether the opposition can capitalise on bitterness over the war.
Divided and lacking a charismatic leader, Georgia's opposition has repeatedly failed to mount a serious challenge since Saakashvili came to power in 2003.
Neither the leading opposition group in parliament, the Christian Democrats, nor Nino Burjanadze, a former parliamentary speaker and a key Saakashvili opponent, said they would join the rally.
Tens of thousands of Georgians took to the streets last year in anti-government protests, forcing Saakashvili to call a snap presidential poll after riot police dispersed demonstrators.
Saakashvili won January's poll in a single round of voting and his United National Movement party swept parliamentary elections a few months later.