Crosslinked chitosan microspheres (CCS) were prepared by emulsion crosslinking, their surface was then grafted with poly(ethylenimine) (PEI) to synthesize a series of PEI modified crosslinked chitosan microspheres (PEI-CCS) with different ion exchange capacities (IEC). The prepared PEI-CCS were characterized, and their static adsorption properties of PEI-CCS to sodium dodecylbenzenesulfonate (SDBS) studied. The results showed that the mean diameter of PEI-CCS was 85 mm. The highest IEC of PEI-CCS reached 1275 mmol/g, being much higher than that of CCS (418 mmol/g). At acidic pH values, the amine groups of PEI-CCS carried positive charges by protonation, and could adsorb anions in aqueous solution. Thus, PEI-CCS exhibited excellent adsorption performance toward SDBS. The adsorption process was spontaneous and exothermic, and well described by the pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity of PEI-CCS increased with increasing of IEC. The maximum adsorption capacity of PEI-CCS-1275 with the highest IEC reached 1487.61 mg/g and was 2.92-fold of CCS (510.20 mg/g). The adsorption capacity of PEI-CCS-1275 was reduced by 17.8% after seven cycles of adsorption-desorption, indicating that PEI-CCS had good reusability for the adsorption of SDBS.