Otto II, Count of Guelders (Dutch: Otto II, Graaf van Gelre) was a nobleman from the 13th century. He was the son of Gerard III, Count of Guelders and Margaretha of Brabant.
After Count William II (1227–1256) was slain in 1256 by Frisians his two-year-old son Floris V, Count of Holland inherited Holland. His uncle (Floris de Voogd regent from 1256 to 1258), and later his aunt (Adelaide of Holland regent from 1258 to 1263) fought over custody of Holland with other nobles. At the battle of Reimerswaal on 22 January 1263, Count Otto II defeated Aleidis and was chosen regent by the nobles who opposed Aleidis.
Otto II served as Floris V's guardian until he was twelve years old (1266) and considered capable of administering Holland himself.