Slovenia is the only EU country that has not yet begun the ratification process.
The two presidents will meet on Saturday after a ceremony at which they and Russian President Vladimir Putin will be named protectors of the European Academy of Sciences and Arts. This title is bestowed on politicians who support the European idea and cooperation in Europe.
On Friday, Josipovic will meet with representatives of the 50,000-strong Croat community in Austria.
His meeting with Pahor will be their first since Pahor was elected president in December.
Slovenia is making the ratification of Croatia's EU accession treaty conditional on the settlement of the Ljubljanska Banka issue. Earlier this month, Pahor said after a meeting with the parliamentary party leaders that all Slovenian parties supported the ratification provided that an agreement was reached on the bank issue.