The poor West African country of some 13 million has seen Online Cigarettes Store USA rolling demonstrations since last month over suspicions that the 81-year-old president is manoeuvring to seek a third term in office.
At least 20 civilians have been killed since mid-October and one gendarme has also been killed.
A Guinean court handed down jail terms to several opposition leaders in October.
On Tuesday, opposition leader Cellou Dalein Diallo could be seen in the middle of the crowd on the hood of a 4x4 vehicle.
Leading civil society members including a top lawyer and a former defence Newport Cigarettes Shop minister took part in the protest.
Schools and shops were shut across much of capital, and security officers were out in force, although they maintained a low profile, an AFP journalist said.
Conde, whose second term ends next year, launched constitutional consultations in September, saying the former French colony's basic law "concentrates corporate interests" and needed reform.
But his adversaries say the president will try to push through an amendment allowing him to Cheap Newport 100s cigarettes seek a third term in elections due in 2020. He has neither confirmed nor denied his intentions.
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