Abstract: In order to improve the stability of astaxanthin,the starch- graft- poly( methyl methacrylate) nanoparticles were synthesized,and then nanoparticles loaded with astaxanthin were prepared by the dialysis method.IR spectra of the starch and the graft copolymer,the average particle size,particle size distribution,and morphology of the nanoparticles loaded with astaxanthin were measured. The stability of nanoparticles loaded with astaxanthin was determined with an acetone solution of astaxanthin as a comparison.The results showed that the average particle size and polydispersity indexof staxanthin nanoparticles were( 208.1 ± 26.4) nm and 0.284 ± 0.035 respectively.The astaxanthin retention rate of nanoparticles was 26.34% after 4 h under artificial lighting.It was 91.81% and 83.44%after storage 8 days at 30 ℃ and 50 ℃ respectively,in the dark under same temperature conditions.It was 86.18%on average at p H1,3,5,7,9 or 11 conditions.