Cyworld (Hangul: 싸이월드) is a South Korean social network service operated by SK Communications (Hangul: SK커뮤니케이션즈), a subsidiary of SK Telecom (Hangul: SK텔레콤).

Members cultivate relationships by forming Ilchon (Hangul: 일촌, Hanja: 一寸) or "friendships" with each other through their minihompy.

Avatars and "mini-rooms", small, decorate-able, apartment-like spaces in an isometric projection, also feature. All of this can make for a Sims-like experience.

The "Cy" in Cyworld could mean "cyber" but is also a pun on the Korean word for relationship (Hangul: 사이 'between').

Revenue is generated through the sale of dotori (Hangul: 도토리), or "acorns", which can then be used to purchase virtual goods, such as background music, pixelated furniture and virtual appliances.

Cyworld also has operations in China and Vietnam.

Launched in 1999, Cyworld was purchased by SK Communications in 2003 and became one of the first companies to profit from the sale of virtual goods.

Cyworld soon became wildly popular in its home market with 2005 claims that practically every South Korean in their 20s and 25 percent of the total population of South Korea were users. By 2006 its domestic user-base numbered 19 million, but this had dropped to 18 million by 2008.