Antunovic told reporters that Racan had left an indelible mark on the creation and development of the independent and democratic Croatia.
"He was a true Social Democrat, a modest man and a fair politician. He opened Croatia's door to Europe and the West, " Antunovic said, adding that Racan was a staunch advocate of human rights and freedoms as well as gender, ethnic and religious equality.
Many SDP members and sympathisers as well as citizens and politicians from other political parties have signed the book of condolence in the SDP headquarters.
A black flag was hoisted outside the SDP main offices on Sunday morning after news of Racan's death was released.