Ottenby is a town on the island of Öland, Sweden, located in Ås parish, Mörbylånga Municipality in Kalmar County. Ottenby is located just north of the southern tip of Öland, over three miles south of the area's main town, Mörbylånga. Ottenby is also the name of the mansion and a royal demesne, now a nature reserve.
Sweden's tallest lighthouse, Långe Jan, is just south of Ottenby.
Ottenby is the name of a mansion (see ) and the nearby nature reserve, formerly a royal game reserve stocked with fallow deer, and King Charles X Gustav of Sweden built a drystone wall to confine the native deer. The reserve is situated at the southern edge of the Stora Alvaret, a unique limestone pavement ecosystem designated as a World Heritage Site comprising most of the southern half of the island of Öland. Ottenby offers diverse habitats including coastal marsh, marine, woodland and alvar. Nearest villages include Alby, Hulterstad, Gettlinge, and Triberga.
Ottenby's name is first mentioned in writing year in 1282. In the Middle Ages it comprised 19 gardens and belonged to Nydala Abbey in Småland. After the abbey's appropriation by Gustav Vasa in the 1520s the mansion became the site of a stud farm; from 1831 to 1892 it was a stud farm for the Swedish army, and later a business.