The Swedish prosecution authority said a total of seven witnesses had been interviewed over the summer.
"We have mainly re-interviewed those individuals who were interviewed in 2010, although two of the persons interviewed have not previously been interviewed," the deputy director of public prosecution, Eva-Marie Persson, said.
The Swedish investigation concerns events which took place in August 2010 when a Swedish woman accused Assange of rape, after meeting him at a WikiLeaks conference in Stockholm.
Assange, 48, has always denied the allegation.
The statute of limitations in the case expires in August 2020.
"Once we have analyzed the interviews, I will decide how to proceed with the case. The investigation may then be discontinued or I may decide to conduct further inquiries," said Persson.
"If I make the assessment that the next step is to interview Julian Assange, I will issue a European Investigation Order, in which case I shall write to the British authorities with a request to conduct an interview," Persson said.
TIMELINE: The key points in the Julian Assange case
Assange has been held at a top-security British prison since April after police sensationally dragged him out of the Ecuadorian embassy in London, where he had been holed up since 2012 to avoid an extradition order to Sweden, where he was wanted for questioning.
Assange was subsequently sentenced to 50 weeks in prison for breaching bail conditions when he took refuge in the embassy.
Following his arrest, Swedish authorities reopened their 2010 rape investigation, which had been closed in 2017 with the argument that it was not possible to proceed with the probe as Assange could not be reached.
Prosecutors then asked a Swedish court to order Assange detained in Sweden in order to facilitate their investigation. But the court refused the request, saying he was already imprisoned in Britain and their investigation could proceed in other ways.
Assange is currently also the subject of a US extradition request, where he is facing a total of 18 charges, most of which relate to obtaining and disseminating classified information over the publishing of military documents and diplomatic cables through the website WikiLeaks.
He could be sentenced to 175 years in prison if convicted on all 18 counts.