This study is on the relationships between the abundances, of cnidarians and echinoderms found in Çardak Lagoon and environmental variables. The benthos samples were collected in three replicates in October 2018, February, April, and June 2019, using a metal framed quadrat system of 100 x 100 cm and 393 cm3 sediment core by a SCUBA diver. Sediment material was collected at 7 sampling points of Çardak Lagoon in Çanakkale Strait. A total of 259 individuals belonging to phylum, Cnidaria and Echinodermata were found in the study area. Cnidarian, Actinia sp. and echinoderm, Asterina gibbosa were the most dominant species. The highest positive correlation value was between Cnidaria species number and organic matter (OM%) content in the sediment. The highest negative correlation value was between Echinodermata species number and NO2+NO3 in lagoon system.