The red macroalga Mastocarpus sp. (Rhodophyta, Gigartinales) has been reported as a non-indigenous species in central Chile. In this area the geographic range described for the species encompasses approximately 200 km, from Cobquecura (36°08'S, 72°48'W) up to Punta Lavapié (37°08'S, 73°35'W). Observations carried out at 22 localities along the central-southern Chilean coast allow us to extend the known range of this species approximately 300 km to the north and 600 km to the south. Additional analysis indicated high percentage cover on areas described as the introduction point of the species.