The aim of this work was to isolate and identify the compounds of the essential oils of sea fennel (Crithmum maritimum L.) and associated hydrolates of plants collected from the area of Brest in France and Ţaborić in Croatia. Isolation of volatile compounds from essential oils was performed by water distillation in a Clevenger apparatus, while the analysis of volatile hydrolate compounds was performed by solid-phase microextraction methods of peak vapors on the solid phase and liquid-liquid extraction using dichloromethane. A gas chromatography-mass spectrometry (GC-MS) system was used to analyze all samples, allowing precise separation and identification of the compounds. In the essential oil of sea fennel from Brest, the most abundant compounds are dillapiol (62,10%), thymyl methyl ether (18,00%) and γ-terpinene (9,88%), while in the essential oil of sea fennel from Šibenik (Ţaborić) the most abundant compounds are limonene (62,85%), sabinene (13,13%) and α- pinene (3,51%). The analysis of the hydrolate from Brest obtained by solid-phase microextraction method (SPME) shows that dillapiol (60,81%) and thymyl methyl ether (14,84%) are the dominant compounds, while in the hydrolate from Ţaborić obtained by the same method terpinene-4-ol (47,46%) and (Z)-carveol (8,01%) dominate. The hydrolates were also prepared for analysis by liquid-liquid extraction with dichloromethane, whereby the analysis revealed the compound dillapiol (85,81%) with a high percentage in the hydrolate from Brest, and the most abundant compound in the hydrolate from Ţaborić was terpinene-4- ol (23,47%). The results of this study show that there are differences in the composition of the essential oils and hydrolates of sea fennel collected from two locations, suggesting that different environmental conditions contribute to differences in the chemical composition of the same plants. These differences in composition may have important implications for the use of sea fennel in the food industry, cosmetics and medicine, depending on the specific properties of the compounds present. The data obtained will form a basis for further research and the possible development of new products based on sea fennel.