Alastaro () is a former municipality of Finland. It was merged into the town of Loimaa on 1 January 2009.
Alastaro is located in the province of Southern Finland and is part of the Southwest Finland region. The municipality had a population of 2,910 (31 December 2008) and covered an area of of which 1.32 kmò is water. The population density was 11.33 inhabitants per kmò.
The municipality was unilingually Finnish.
The Alastaro Circuit opened in 1990.