The Slovene Democratic Party (German: Slowenische Demokratische Partei), or SDP, is a now-defunct Austrian political party that existed between 1980 and 1995, when it merged with the Party for Istria to form the Democratic Party. The SDP was the federal sister party of the Slovene-nationalist Carniola Party (Krain Partei) that ruled the province of Carniola between 1984 and 2008.
The SDP was an explicitly autonomist party advocating broader autonomy for the Slovene-majority province of Carniola, with a right-nationalsit wing that advocated a full separation from Austria and a left-autonomist wing with a close relationship to the federal Social Democrats. The party enjoyed membership from all ends of the political spectrum as its main message was one of empowerment for the Slovene majority in the province, which by the early 1980s had grown economically disadvantaged. The party won eleven seats in the 1983 federal elections, helping defeat the SPÖ which had traditionally enjoyed Carniola being part of its base of support, and it elevated the SDP as a major political player. The party had its best showing in 1987 when it swept Carniola's seats, including the seat of then-SPÖ leader. This showing, netting the party Carniola's 34 seats, initiated the sovereignty debate of the late 1980s which helped lead to the rise of the NVP. The SDP lost fourteen seats in the 1990 elections and a further eight seats in the 1994 polls, dropping them to twelve seats. In 1995, they merged with the Croatian-dominant Party for Istria to form the minority-rights Democratic Party.
The party was led for the entirety of its existence by Milan Kučan, who opposed the merger with Party for Istria (PFI) and instead became head of the KP in 1995, serving as the Staatsminister for Carniola from 1995 until 2001.