The Social Democratic Party (SDP) is a political party in Taiwan founded in 2015. In 2015, the SDP formed a coalition with the Green Party Taiwan to contest the 2016 legislative election.
Historically, the SDP is one of Taiwan's "Third Force" () parties, a collection of parties that do not self-claim to either the Pan-Green or Pan-Blue Coalitions and tend to be rooted in social movements. Currently, the SDP has become part of the Pan-Green camp, with more Taiwanese nationalist positions accepted and working with the Democratic Progressive Party.
The SDP is a social-democratic and progressive party, calling for a reduction in income inequality, the protection of labour rights, the abolition of the death penalty and the legalisation of same-sex marriage. The party has also called for a reform to Taiwan's electioneering process, criticising the advantage given to parties with big financial backers.
In the 2016 legislative election, the SDP ran in a coalition with the Green Party Taiwan, garnering 2.5% of the vote and winning no seats.
In the 2018 local elections, SDP candidate Miao Po-ya won a seat on the Taipei City Council. She is one of the first openly lesbian members of the municipal council.