This study aimed to investigate the total phenolic content (TPC), the identification of the common compounds by HPLC-ESI-MS and HPLC-ESI-MS-TOF and the inhibitory effects against class A-type beta-lactamase (GES-22 variant, produced recombinantly) in methanolic extracts (MEs) of four Algerian seaweeds [Ulva intestinalis, Codium tomentosum, Dictyota dichotoma and Halopteris scoparia]. The TPC varied among the four species, ranging between 0.93 +/- 0.65 and 2.66 +/- 1.33 mg GAEs/g DW. C.tomentosum had higher total phenol content than other seaweeds while, all of them inhibited uncompetitively GES-22 activity in a dose-dependent manner. Nitrocefin was used as chromogenic substrate to evaluate the inhibitory effect on GES-22. The methanolic extract of D.dichotoma exhibited significant inhibitory effect on GES-22 (IC50 = 13.01 +/- 0.046 mu g/mL) more than clavulanate, sulbactam and tazobactam (classical beta-lactam inhibitors) (IC50 = 68.38 +/- 0.17 mu g/mL, 52.68 +/- 0.64 mu g/mL, and 29.94 +/- 0.01 mu g/mL, respectively). IC50 of the other ME of U.intestinalis, C.tomentostum, and H.scoparia were 16.87 +/- 0.10 mu g/mL, 16.54 +/- 0.048 mu g/mL, and 25.72 +/- 0.15 mu g/mL, respectively. Except H. scoparia, other three seaweed extracts showed almost two times or more inhibition on GES-22. Furthermore, four common compounds in these MEs were identified, alpha-linolenic acid (C18:3 omega 3), linoleic acid (C18:2 omega 6), oleic acid (C18:1 omega 9), the eicosanoid precursors "arachidonic acid" (C20:4 omega 6). Baicalein (C15H10O5) was identified in U.intestinalis and D.dichotoma seaweeds. The fact that all seaweed extracts inhibited the GES-22 better than commercial samples makes these seaweeds candidate for discovering new inhibitors against beta-lactamases. Besides that, they contain important components with potential health benefits.