Cholesterol modified alginate (CSAD) was prepared by DCC/DMAP covalent attachment of hydrophobic cholesterol onto the nature polysaccharide alginate. And the nanocapsules loaded cyhalothrins were obtained by emulsification method. The structure and hydrophobic properties of the alginate derivative and the morphology and release properties of the nanocapsules were characterized by means of Fourier transform infrared spectroscopy (FTIR), 1H Nuclear Magnetic Resonance (1H NMR), fluorescence spectrum, dynamic light scattering, transmission electron microscopy (TEM) and release studies. Experimental results showed that the degree of substitutions of CSAD were 5.3%~7.9% and their critical aggregation concentration were reduced from 1.23 mg/L to 0.26~0.63mg/L. With increasing degree of substitution, the hydrophobic group increased and the critical aggregation concentration reduced. The d50 of the drug-loaded nanocapsules were 576.4 ?7.4nm, and the Zeta potential value of drug-loaded nanocapsules were -32.3 ?0.6mV, which could exhibit excellent stability in aqueous solution. Compared with conventional microemulsions, the hydrogen bonds were key to CSAD to possess the Slow-Release properties.