乌溪沙（英语：Wu Kai Sha）原称乌龟沙，位于香港新界沙田区，邻接马鞍山，为香港一处郊游度假地点，近年发展成为住宅区域。

考古学家在马鞍山及乌溪沙一带发现有新石器时代后期的文物遗迹，证明乌溪沙在当时已经有人类居住。

早年，乌溪沙十分偏僻，无道路直接抵达，当时对外交通依赖街渡，由港铁大学站侧的马料水码头前往乌溪沙。

1980年代末期，香港政府开发马鞍山新市镇，在沙田开辟了多条道路通往马鞍山及乌溪沙，亦开辟了通往西贡区的西沙路，从此乌溪沙的交通变得方便。此外，同段时期，为了应付当时严重的越南船民问题，香港政府在乌溪沙兴建白石船民中心为难民营，当年曾经在此发生过多次骚乱及武装冲突，随着越南船民问题于香港回归前解决，船民已经被遣返越南，白石船民中心亦被拆卸，更改兴建成为高尔夫球场等康乐用途设施。

Wu Kai Sha (Chinese: 烏溪沙), formerly known as Wu Kwai Sha or U Kwai Sha (烏龜沙), is a place at the shore of Tolo Harbour, northwest of Ma On Shan in the New Territories, Hong Kong. Wu Kai Sha is within the Shatin District, one of the 18 districts of Hong Kong. It is famous for a campsite, Wu Kai Sha Youth Village of YMCA. Originally there were only a few villages like Wu Kwai Sha Village. It is now an extension of a new town in Ma On Shan. There is also a beach near the Wu Kai Sha Youth Village.