Sia Wai Yen (born 15 January 1984) is a Malaysian swimmer who specialised in long-distance freestyle and individual medley events.

Sia competed in a medley double at the 2000 Summer Olympics in Sydney.

In heat four, she finished at the bottom of the pack in a poor time of 4:59.18, more than six seconds slower than her national record.

[5][6][7] Two days later, in the 200 m individual medley, Sia posted a time of 2:20.64 in heat two but finished in thirty-first place among 36 other swimmers from the prelims.

[11][12] At the 2002 Asian Games in Busan, South Korea, Sia finished seventh in the 400 m individual medley at 5:06.20, holding off a sprint freestyle race from Hong Kong's Chan Wing Suet by four-hundredths of a second (0.04).