Belgian prosecutors believe they may have found a bomb factory also used as a hideout by one of the jihadists after the Paris attacks.
Police found traces of explosives, three handmade belts and a fingerprint of fugitive Salah Abdeslam.
The apartment in the Schaerbeek district of Brussels had been rented in a false name that might have been used by a person already in custody.
Islamic State (IS) suicide attackers killed 130 people in the attacks.
Traces of the explosive TATP (acetone peroxide) and the belts, which could have been used to transport explosives, were found in the raid on 10 December in Rue Berge, the Belgian federal prosecutor's office said.
The prosecutor's office told the BBC that Abdeslam's fingerprint was not dated, and it would be very hard to determine the date.
Prosecutors believe that the Schaerbeek flat was used only by the Belgium-based attackers who went to the apartment, got the explosive belts, and then went to Paris.
However, they believe that Abdeslam, 26, did go back to the flat in Schaerbeek because he probably thought it would be the only place where he could be safe after the attacks.
Their theory is that somebody drove him there, and dropped him not far from that Schaerbeek address, right after the Paris attacks.
French police pulled over the VW Golf car he was travelling in with two others near Belgium, but then let the group continue their journey.
Abdeslam is believed to have rented a VW Polo car in Belgium, which was later found near the Bataclan concert hall in Paris where 89 people were killed. But he also rented a Renault Clio and reserved two hotel rooms outside Paris before the attacks.
His precise role in the attacks themselves is unclear. Although his brother Brahim blew himself up, Salah Abdeslam is thought to have played a logistical role.
The Paris attacks are believed to have been at least partly planned in Brussels. Belgian police have arrested 10 people in the investigation, including one who rented the apartment in Schaerbeek. The district is central, just north of the EU institutions.
Among the 10 held are Mohammed Amri et Hamza Attou, suspected of having brought Salah Abdeslam back to Brussels from Paris.
Immediately after the attacks, the police focused their searches on Molenbeek, in western Brussels, where some of the attackers were known to have lived.
The suspected ringleader was Abdelhamid Abaaoud, a Belgian national. He and his cousin Hasna Aitboulahcen died in a fierce gun battle five days after the attacks, when police raided a flat in Paris where they were hiding, heavily armed.
The search for Abdeslam
- Hours after the 13 November attacks, Salah Abdeslam's VW Golf car was pulled over by French police on the A2 motorway near the Belgian border, but was released after checks
- It is unclear whether police had linked a VW Polo found at the Bataclan venue to him by this time
- Police issued an arrest warrant on 15 November
- Unconfirmed reports said he was spotted by police in the Belgian city of Liege, heading towards Germany, on 15 November but escaped in a black BMW
- A raid on a suspected hideout in Molenbeek, Brussels, later that day was delayed because of a ban on night-time searches
- Friends told media the suspect was hiding in Brussels and desperately trying to get to Syria
- Undated fingerprint from Abdeslam found in a flat in Rue Berge, in the central Brussels neighbourhood of Schaerbeek, on 10 December
- Police believe Belgian attackers picked up explosives belts from Schaerbeek flat before Paris attacks and Abdeslam returned there afterwards