Former Catalonia vice-president Oriol Junqueras, former cabinet member Joaquim Forn and two leaders of civic groups ANC and Omnium Cultural, facing charges of sedition, have been refused bail.
Six other former members of the Catalonia cabinet, detained in custody ahead of an investigation into their part in an illegal unilateral declaration of independence by the then-regional government October 27, were set bail of 100,000 euros ($A165,998).
The Catalan leaders' organisation of an independence vote October 1 and the subsequent declaration of independence, both acts banned under Spain's constitution, have tipped the country into its worst political crisis in more than four decades.
The central government sacked the previous government within hours of the declaration and called a regional election for December 21.
The eight former members of the cabinet were detained in custody November 2 facing potential charges of sedition, rebellion and misappropriation of funds. They have since called to be released to campaign for the election.
The former leader of the Catalonia government, Carles Puigdemont, and four of his disbanded cabinet, are in self-imposed exile in Belgium under conditional release after an international arrest warrant was served against them.
Puigdemont arrived Monday for an extradition hearing in Belgium as Spain seeks to have him sent back to face sedition charges over his region's independence drive.
His lawyers later confirmed the judge will hand down the extradition decision on December 14.
Prosecutors last month asked the judge to approve the European arrest warrant issued by Madrid for the five in the opening round of what could become a protracted courtroom battle.
On Monday, Spain's Supreme Court refused bail for Junqueras, Forn and leaders of Catalan civic groups Asamblea Nacional Catalana (ANC) and Omnium Cultural, Jordi Sanchez and Jordi Cuixart.
In a court statement, the judge ruled that, while he considered there was no risk the defendants would leave the country, he did believe there was a risk of criminal reiteration.
Campaigning for the election, with Junqueras at the head of the list for his party ERC, begins on Tuesday and polls have shown that support for independence is running in a dead heat with support for continued unity with Spain.
