This study describes the occurrence of the toxic dinoflagellate Gymnodinium catenatum bloom in Libyan Mediterranean coastal water. G. catenatum exhibited high abundance (3.5x105 cells L-1) in Tajoura coastal water during September 2023. The high abundance of  G. catenatum associated with the increase in nutrient concentrations in sea water caused by anthropogenic discharge. Cysts of  G. catenation were also identified (125 cysts g‑1) in sediment samples collected from the study area during the bloom event. The analysis of high-performance liquid chromatography with fluorescence detection (HPLC-FLD) revealed that of G. catenatum bloom was able to produce paralytic shellfish toxins (PSTs) with a profile consisting of saxitoxin (STX), decarbamoyl-STX (dcSTX), neosaxitoxin (NeoSTX), gonyautoxin-1 (GTX1), GTX2, GTX3, GTX4, and C1/C2 toxins with varying concentrations (11.2, 5.3, 3.3, 2.4, 1.9, 18.2, 16.3, 41fg cell-1, respectively). Similarly, a strain culture of G. catenatum isolated from this bloom produced the same toxin profile as the bloom, but with different proportions of toxin variants. Cultured cells produced approximately 1.5 times more toxin than cells from bloom samples. The results of our study contribute to the knowledge of the toxicity of G. catenatum bloom in Libya coastal waters and provide valuable information on the persistence of G. catenatum cells and cysts which could lead to yjr bloom recurring in the water column. Therefore, the study suggests monitoring programmes for harmful dinoflagellates and their cysts in Libyan coastal waters to protect the marine ecosystem and seafood animals from exposure to such potent toxins.