Sebastian Fabian Klonowic (1545 Sulmierzyce – 29 August 1602 Lublin) was a Polish poet, composer and mayor of Lublin.

He studied at the University of Kraków. He was also known by his Latin name, Acernus, and wrote in both Polish and Latin.^[1] He first lived in Lwów, then he settled in Lublin. While in Lublin, he became mayor.

He wrote attacks in Latin on the Jesuits. His Latin poems were filled with Latinized Polish words, and on the other hand his Polish poems were often made unintelligible by the use of Latinisms and Hellenisms literally translated. He lived his last years on the charity of the Jesuits.^[1]

• Roxolania (1584) — a description the people and land of Ruthenia
• Flis, to Jest Spuszczanie Statków Wisłą (1595) — an early example of the Sapphic stanza in Polish poetry, exceptional for its length
• Worek Judaszów (1600)
• Victoria Deorum (1587)
• Żale nagrobne na ślachetnie urodzonego Pana Jana Kochanowskiego
• Gorais
• Hebdomas, to jest Siedem tegodniowych piosnek wyjętych z pierwszych Ksiąg Moiżeszowych kapituły pierwszej, co którego dnia Pan Bóg stworzył i jako siódmego dnia odpoczynął, krótko zebranych przez Sebastyjana Klonowica z Sulimierzyc, pisarza ławicy lubelskiej (1581) — songs