Clashes broke out in front of the Senate in Buenos Aires on Thursday morning, after a bill to legalise abortion in the first 14 weeks of pregnancy was rejected by a narrow 38:31 vote.
Campaigners for the bill were outside the Senate during the 12-hour long session and tensions arose once the result was announced.
Police barricaded the Senate and made use of water cannons against enraged protesters who hurled objects at them.
Senators rejected the bill by a seven vote margin, 38:31, with two abstentions.
The bill had not been supported by President Mauricio Macri.
Pro-choice supporters in Argentina had been rallied by legislative success in other predominantly Catholic countries such as Ireland, but in Latin America only three other states; Uruguay, Guyana and Cuba, permit early-term abortions.