John I of Opava-Ratibor (Czech: Jan I. Ratibořský; German: Johann I. von Troppau-Ratibor; c. 1322 – c. 1380-1382) was the founder the Opava branch of the Bohemian Přemyslid dynasty, which lasted until 1521.

From 1367 to 1377 he ruled the Duchy of Opava (German: Troppau) jointly with his brothers, Nicholas III, Wenceslaus I and Przemko I.

In 1377, a new division was made, in which John I kept Racibórz, but also received the duchies of Krnov and Bruntál.

The Duchy of Głubczyce was split off for Nicholas III; Wenceslaus I and Přemysl received the rest of Opava.

Because of financial difficulties, he sold Mikołów and the Principality of Pless to Duke Władysław II of Opole in 1375.