High quality Zn0.5CovFe2.5-xO4(x = 0,0.05,0.1,0.15)serial magnetic nanoparticles with single cubic structures were prepared by the modified thermal decomposition method,and Zn0.5CoxFe2.5-xO4/SiO2 composite magnetic nanopar-ticles were prepared by surface modification of SiO2.The magnetic anisotropy of the sample increases with the increase of the doping amount of Co2+.When the doping amount is 0.1,the sample shows the transition from superparamagnetism to ferrimagnetism at room temperature.In the Zno.5CoxFe2.5-xO4/SiO2 serial samples,the maximum value of specific loss power(SLP)with 1974 W/gmeta]can also be found at doping amount of x = 0.1.The composite nanoparticles are expected to be an excellent candidate for clinical magnetic hyperthermia.