Omobranchus sewalli is a native Indo-Pacific blenniid recently introduced and established along the Brazilian coast. The putative introduction was through ballast water and/or ship hull biofouling. Herein, we report the presence of the species for the first time inside of the Paranaguá Estuarine Complex (PEC) which is recognized as a RAMSAR site and listed as a Wetland of International Importance. The mature specimens of O. sewalli were found in intertidal and shallow subtidal waters in the mixture zone in the estuary, suggesting the establishment of the population. The presence of port terminals in this area indicates that O. sewalli colonize PEC using ship hull fouling or larval dispersal from the shallow inner shelf.