Predmet istraživanja ove doktorske disertacije su tri morske alge: Halimeda tuna (J. Ellis & Solander) J.V. Lamouroux (Halimedaceae), Codium bursa (Olivi) C. Agardh (Codiaceae), Cystoseira barbata (Stackhouse) C. Agardh (Sargassaceae) i morska trava Cymodocea nodosa (Urcia) Ascherson (Cymodoceaceae) iz Jadranskog mora. Nutritivna vrednost odabranih uzoraka je ispitivana korišćenjem zvaničnih AOAC (Association of Official Analytical Chemists) metoda. Najveću energetsku vrednost, u navedenim ispitivanjima, imala je zelena alga C. bursa (490,4 kcal). Metodom hladne maceracije u trajanju od 48 sati, dobijena su tri polarna ekstrakta: dihlormetan : metanolni (1:1) (DME), 70% metanolni i vodeni ekstrakt. Suvi ekstrakti su dalje korišćeni za biološka in vitro ispitivanja kao što su: antioksidativna, antimikrobna, anti α- glukozidazna i citotoksična aktivnost. DME ekstrakt H. tuna je pokazao najbolju citotoksičnu aktivnost prema ćelijama humanog karcinoma kolona, LS174 (IC50=17,92 ± 1,54 μg/ml). DME ekstrakt C. nodosa je pokazao snažnu citotoksičnu aktivnost prema ćelijama humanog adenokarcinoma, HeLa (IC50=13,28 ± 0,39 μg/ml) i prema ćelijama humane hronične mijelogene leukemije, K562 (IC50=19,64 ± 1,55 μg/ml). Najbolju anti α-glukozidaznu aktivnost (IC50=9,98 ± 3,34 μg/ml) i najbolju antibakterijsku aktivnost (MIC 100 μg/ml) prema Staphylococcus aureus i Bacillus subtilis je ispoljio DME ekstrakt C. barbata. Razvojom odgovarajuće HPLC metode, kao i primenom odgovarajućih metoda detekcije identifikovana su tri jedinjenja (diosmetin-7-sulfat, kaftarinska i kutarinska kiselina) u DME ekstraktu morske trave C. nodosa. Sadržaj β-glukana, masnih kiselina, sterola i mikro- i makroelemenata je ispitivan u svim navedenim uzorcima. Najveći sadržaj β-glukana bio je u morskoj travi C. nodosa (13,04 ± 0,42 g/100 g). C. nodosa, morska trava, pokazala je najviši sadržaj polinezasićenih masnih kiselina (PUFA, 7,157 mg/g). Značajan sadržaj sterola (fukosterol, 21,76 ± 0,1 μg/g) i najbolji odnos polinezasićenih i zasićenih (SFA) masnih kiselina, PUFA/SFA (0,08) pokazan je kod mrke alge C. barbata. Zelene alge, C. bursa i H. tuna, imale su najveći saržaj sterola (β- sitosterol, 95,21 ± 0,16 μg/g i 73,90 ± 0,08 μg/g, respektivno). Najviši sadržaj kalcijuma (Ca), u količini od 55125 μg/g, detektovan je kod alge H. tuna. The research subject of doctoral dissertation were three seaweeds: Halimeda tuna (J. Ellis & Solander) J.V. Lamouroux (Halimedaceae), Codium bursa (Olivi) C. Agardh (Codiaceae), Cystoseira barbata (Stackhouse) C. Agardh (Sargassaceae) and the one seagrass Cymodocea nodosa (Urcia) Acherson (Cymodoceaceae) from the Adriatic Sea. Nutritional value of selected samples were investigated by official AOAC (Association of Official Analytical Chemists) methods. The highest energy value had the green seaweed C. bursa (490,4 kcal). Using the cold maceration extraction, lasting 48 h, the three polar extracts were obtained: dichlormetan: methanol (1:1) (DME), 70 % methanol and aquous extracts. The dry extracts were further used for biological in vitro investigations, such as: antioxidative, antimicrobial, anti α-glucosidase and cytotoxic activity. DME extract of H. tuna has shown the best cytotoxic activity against human colon carcinoma cell line, LS174 (IC50=17,92 ± 1,54 μg/ml). DME extract of C. nodosa had strong cytotoxicity against human adenocarcinoma cell line, HeLa (IC50=13,28 ± 0,39 μg/ml) and human chronic myelogenous leukaemia cell line, K562 (IC50=19,64 ± 1,55 μg/ml). The best anti α-glucosidase (IC50=9,98 ± 3,34 μg/ml) and best antibacterial activity (minimal inhibitory concentration of 100 μg/ml) for Staphylococcus aureus and Bacillus subtilis was demonstrated in DME extract of seagrass C. nodosa. Developing the appropriate HPLC method, accompained with the appropriate detection methods, the three compounds were identified (diosmetin-7-sulfate, caftaric and coutaric acid) in the DME extract of seagrass C. nodosa. The content of β-glucan, fatty acids, sterols and micro- and macroelements were investigated in all samples. The highest content of β-glucan was detected in C. nodosa seagrass (13,04 ± 0,42 g/100 g). C. nodosa had also the highest level of polyunsaturated fatty acids (PUFAs) (7,157 mg/g). Significant sterol content (fucosterol, 21,76 ± 0,1 μg/g) and the best ratio of polyunsaturated and saturated (SFA) fatty acids, PUFA/SFA (0,08) was shown in C. barbata, brown seaweed. Green algae, C. bursa and H. tuna, showed the highest level of sterols (β-sitosterol, 95,21 ± 0,16 μg/g and 73,90 ± 0,08 μg/g, respectively). H. tuna had the highest content of calcium (Ca) in amount of 55125 μg/g.