| Birth Place: | Apia, Samoa |
| Birth Date: | 1977 9, df=yes |
| Weight: | 246 lb |
| Position: | Flanker |
| Amatteam1: | Manurewa |
| Amatteam2: | Ponsonby RFC |
| Amatyears2: | -2003 |
| Years1: | 2003–2004 |
| Years2: | 2004–2006 |
| Years3: | 2006–2007 |
| Clubs1: | Exeter Chiefs[1] |
| Clubs2: | Worcester Warriors[2] |
| Clubs3: | Viadana Rugby[3] |
| Apps2: | 27 |
| Points2: | 20 |
| Provinceapps1: | 1 |
| Provinceapps2: | 1 |
| Provinceyears1: | 2000 |
| Provinceyears2: | 2002 |
| Provincepoints1: | 5 |
| Provincepoints2: | 0 |
| Province1: | Counties Manukau[4] |
| Province2: | Hawkes Bay |
| Repyears1: | 2001–2004 |
| Repcaps1: | 10 |
| Reppoints1: | 0 |
Siaosi Vaili (born 7 September 1977) is a Samoan former rugby union player. He played as a flanker.
Vaili was born in Apia, Western Samoa. He moved to New Zealand playing for the provincial teams of Counties Manukau and Hawke's Bay. In the summer of 2003, he arrived in Europe, playing for the Exeter Chiefs, in the English second division. A season later, Vaili joined Worcester Warriors in the English Premiership, where he stayed for two seasons until 2006; and a year later, for Viadana Rugby, with which he won the 2006-07 Coppa Italia.
He first played for Samoa in a test match against Ireland, at Lansdowne Road, on 11 November 2001, during the Samoa tour of Europe in 2001. He was part of the 2003 Rugby World Cup roster, playing only the match against Georgia. His last international cap was against Fiji, at Suva, on 12 June 2004.