Aim: In the continuing search for safe and efficient antidiabetic drug, marine algae become important source which provide several compounds of immense therapeutic potential. Alpha-amylase, alpha-glucosidase inhibitors, and antioxidant compounds are known to manage diabetes and have received much attention recently. In the present study, four green algae (Chaetomorpha aerea, Enteromorpha intestinalis, Chlorodesmis, and Cladophora rupestris) were chosen to evaluate alpha-amylase, alpha-glucosidase inhibitory, and antioxidant activity in vitro. Materials and Methods: The phytochemical constituents of all the extracts were qualitatively determined. Antidiabetic activity was evaluated by inhibitory potential of extracts against alpha-amylase and alpha-glucosidase by spectrophotometric assays. Antioxidant activity was determined by 2,2-diphenyl-1-picrylhydrazyl, hydrogen peroxide (H 2 O 2 ), and nitric oxide scavenging assay. Gas chromatography-mass spectrometry (GC-MS) analysis was carried out to determine the major compound responsible for its antidiabetic action. Results: Among the various extracts screened, chloroform extract of C. aerea (IC 50 − 408.9 mg/ml) and methanol extract of Chlorodesmis (IC 50 − 147.6 mg/ml) showed effective inhibition against alpha-amylase. The extracts were also evaluated for alpha-glucosidase inhibition, and no observed activity was found. Methanol extract of C. rupestris showed notable free radical scavenging activity (IC 50 - 666.3 mg/ml), followed by H 2 O 2 (34%) and nitric oxide (49%). Further, chemical profiling by GC-MS revealed the presence of major bioactive compounds. Phenol, 2,4-bis (1,1-dimethylethyl) and z, z-6,28-heptatriactontadien-2-one were predominantly found in the methanol extract of C. rupestris and chloroform extract of C. aerea. Conclusion: Our results demonstrate that the selected algae exhibit notable alpha-amylase inhibition and antioxidant activity. Therefore, characterization of active compounds and its in vivo assays will be noteworthy.