German ab bet din; born about 1743 at Prague; died 1822 at Hamburg. From 1783 to 1814 he was dayyan in the latter city, and in Jan., 1814, he became president of its rabbinate, at the time when the town was occupied and was being ransacked by the French. After the foundation of the Tempel (1818), Oser protested in the name of the Hamburg rabbinate against the reforms in the service; and he threatened to excommunicate all who should further them. In order to confirm his action he asked the most celebrated Orthodox rabbis for their opinions, and published their answers under the title "Eleh Dibre ha-Berit" (Altona, 1819). In 1821 he resigned on account of old age.
- E. Duckesz, Iwwah le-Moshab, Cracow, 1903;
- Grätz, Gesch. 2d ed., xi. 383 et seq.