Yuko Oshima (born in Tochigi Prefecture) is a member of Japanese idol group AKB48's Team K, and a subunit of the group, Not yet. She has been a contributing member for all of AKB48's singles since "Aitakatta" in October 2006, excluding Janken Tournament singles. In 2009, she was voted second popular and lost to Atsuko Maeda. In 2010, she was voted the most popular member of the group, in a poll for which members fans want to appear on the group's single "Heavy Rotation". However during the 2011 3rd senbatsu election, she lost first place to Atsuko Maeda once again having dropped to second place.
In 1996, Oshima was signed as a child actor, with Central Kodomo Gekidan. In 2005, she began working as a junior idol in the short lived idol project Doll's Vox, produced by The Alfee vocalist Toshihiko Takamizawa. In 2006, at the AKB48's second audition to form Team K, Oshima was selected as one of 17 successful applicants, out of a pool of 12,000 applications. In April, she began working full-time with the group, and featured on the group's first single with DefStar Records, "Aitakatta", in October 2006.