The Kasatura Bay region is one of Türkiye’s Important Plant Areas and plant biodiversity hotspots. In this study, the diversity and gradient of the sand-dune vegetation in Kasatura Bay were studied. Vegetation sampling was carried out by using the Braun-Blanquet method. The vegetation dataset was recorded in the TURBOVEG database management program. For classification, Beta-Flexible clustering (β = −0.25) and the correlation similarity index were used in the PC-ORD program. Diagnostic species of the communities were determined in the JUICE program using the φ-coefficient (higher than 0.30). Detrended Canonical Correspondence analysis was applied to data in the CANOCO program to understand the effect of ecological factors on vegetation diversity. Ellenberg ecological indicator values were used as the ecological variables. As a result, seven different plant communities were identified at the Kasatura Bay sand dunes. A new association of Sileno thymifoliae–Cionuretum erectae ass. nova was identified under the alliance Sileno thymifoliae–Jurineion kilaeae. The sand-dune vegetation represents high diversity, also including endemic plants, some of which are globally threatened. Due to all this diversity, settled on sensitive conditions, conservation strategies need to be developed to protect and ensure the continuity of Kasatura Bay sand-dune vegetation in the face of intense human pressure.