The Communist Party of Slovakia (Slovak: Komunistická strana Slovenska — KSS) was a communist party in Slovakia. It was formed in March 1939, when the Slovak Republic was created, as the Slovak branches of the Communist Party of Czechoslovakia (KSČ) were separated from the mother party. When Czechoslovakia was again established as a unified state, the KSS was still a separate party for a while (1945–1948). On September 29, 1948, it was reunited with the KSČ and continued to exist as an "organizational territorial unit of the KSČ on the territory of Slovakia". Its main organ (and thus the main newspaper in Slovakia at the time) was Pravda.
After the merger KSS functioned as a regional affiliate of the KSČ, not as an independent political institution. Therefore, the organizational structure of the KSS mirrored that of the KSČ: the KSS Congress held session for several days every five years (and just before the KSČ's Congress), selecting its Central Committee members and candidate members, who in turn selected a Presidium, a Secretariat, and a First Secretary (i.e. party leader).
The most important first secretaries were Alexander Dubček (1963–1968) and Jozef Lenárt (1970–1988). Following the March 1986 party congress, the KSS Presidium consisted of 11 members; the Secretariat included, in addition to Lenárt, three secretaries and two members; and the Central Committee comprised 95 full members and 36 candidate members. The KSS in 1986 also had its own Central Control and Auditing Commission, four other commissions, twelve party departments, and one training facility.
KSS ceased to exist in 1990 (following the Velvet Revolution), when it was transformed into the independent Social Democratic party called the Party of Democratic Left. A new Communist Party of Slovakia was, however, founded in 1992.