Benzyl alginate derivative (BAD) was prepared by bimolecular nucleophilic substitution reaction (SN2) using the benzyl bromide as a hydrophobic modifier. The structure and performance of BAD was characterized by FTIR, 1HNMR, TGA, UV-Vis, GPC, DLS and Zeta potential analyzer. Experimental results showed that the degree of substitution of the obtained product (49.21 % and 29.33 %) was close to the molar ratio of benzyl bromide to uronic acid, indicating that SN2 reaction was active with large degree of substitution. After modification, the molecular weight (MW) of BAD decreased from 91544 to 79819. And the micellar aggregates were formed by BAD under hydrothermal driving forces with the hydrodynamic diameter (dH) as 423.4 nm and the zeta potential value as -36.4 mV. Furthermore, with the increase of pH, the Zeta potential of BAD tended to decrease, while its hydrodynamic size (dH) firstly increased and then decreased. Meanwhile, with the increase of ionic strength, the dH and Zeta potential of BAD firstly increase and then decrease, which revealed that BAD may possess certain colloidal and interfacial activity.