Abstract: In this study, the different acid pretreatments(with HCl and H₂SO₄) were applied to compare the sacchariflcation efficiency of Laminaria japonica which including the total reducing sugars and glucose. According to the two indicators, the results showed that the sacchariflcation efficiency from L. japonica that was pretreated with 1% HCl was the highest, with the total reducing sugars 24.16% and glucose concentration 0.32 mg/mL. A new bioflocculant producing bacterium Enterococcus sp. Y025(Genbank: KX950932) could grow and produce bioflocculant using acid pretreated L. japonica as the optimal substrate without the addition of K₂HPO₄ and KH₂PO₄. The cell growth and bioflocculant production of strain Y025 under different volume ratio of hydrolysate(20%, 40%, 60%, 80%, and 100%) were investigated. The result indicated that the optimal volume ratio of hydrolysate was 80%, with high bioflocculant production of 52.91%. Macro-algae such as L. japonica show the prospect of high biomass yields. The result indicated that the strain Y025 has the ability to produce bioflocculant using the acid pretreated L. japonica, which is beneficial for the improvement of cost-effective bioflocculant production.