In this thesis, the structural and magnetic properties of pure and Zn doped cobalt ferrite nanoparticles synthesized in the absence and in the presence of different magnetic field have been investigated. In the first part of this work, Co 0.3 Zn 0.7 Fe 2 O 4 and CoFe 2 O 4 nanoparticles were prepared by using sol-gel method in absence of magnetic field. Then,the nanoparticles were coated with zein biopolymer in an external magnetic field to obtain ordered structure.The resultant zein/nanoparticles films were characterized by XRD, SEM and VSM. The SEM images demonstrated that an ordered structureis formed in the presence of external magnetic field. In the next section of this project, the effect of magnetic field on the structural and magnetic properties of Co 1-x Zn x Fe 2 O 4 (x=0, 0.1) nanoparticles have been investigated. The nanoparticles were synthesized in different synthesizing magnetic field of 0, 0.2, 0.4 and 0.8 Tesla by sol-gel method. The XRD patterns indicated that the single phase spinel structure is formed and the synthesizing field did not affect the crystal structure.The average size of CoFe 2 O 4 nanoparticles obtained using the Scherrer equation increases with increasing magnetic field.The VSM results showed that the saturation magnetization (M s ) of CoFe 2 O 4 nanoparticles increases with increasing magnetic field from 0 to 0.8 T.Unlike the CoFe 2 O 4 , the XRD spectrum confirmed that by applying magnetic field, the single phase spinel crystal structure is not formed in the Zn doped cobalt ferrite (Co 0.9 Zn 0.1 Fe 2 O 4 ). The magnetization hysteresis curves of Co 0.9 Zn 0.1 Fe 2 O 4 nanoparticles showed that by increasing the synthesizing field and destroying the spinel crystal structure, the magnetic pr operties are weakened (the saturation magnetization and remanent magnetization (M r ) are reduced.).