Waving Catalan independence flags of red and yellow stripes overlaid with a white star on a blue background, demonstrators crowded on Sant Jaume square in the northeastern city under umbrellas, yelling "We will vote".
The Constitutional Court on Monday agreed to hear an appeal by the Spanish government against Catalan leaders' plan to hold a vote on independence on November 9.
The decision left protesters feeling bitter and defiant.
"They do not listen and they don't try to understand why so many people are demanding to be able to vote," said one demonstrator in Barcelona on Tuesday, Montserrat Benet, a 51-year-old English teacher. "No law can stop this."
Catalonia's president Artur Mas on Saturday signed a decree calling the referendum, which was automatically suspended under Spain's constitution when the court accepted the appeal on Monday.
The regional government on Tuesday cautiously halted its publicity campaign for the vote so as not to oblige regional servants to break the law, but Catalan separatists vowed to push ahead regardless.
"Not rain nor snow nor any court will stop us," said Carme Forcadell, leader of the Catalan National Assembly, a powerful civil campaign group for independence. "On November 9 we will vote and we will win."