A novel magnetorheological (MR) suspension was based on methyl silicone oil and cobaltphthalocyanine (Co-Pc)/Fe nanocomposite particles, which were synthesized by thermally decomposing liquid carbonyl Fe in the solution of Co-Pc in N, N-dimethyl formamide. The nanocomposite particles were fully characterized by XRD, SEM and HREM, and the thermal, magnetic and MR properties of nanocomposite particles were measured. Such factors as weight percent of particles (w), magnetic field strength (H), temperature (T) and shear rate (γ) etc influencing on MR properties were investigated. The results indicated that Co-Pc/Fe nanocomposite with density of 3.66 g/cm3 was almost micro-sized regular spheroids consisting of tens of Co-Pc coated α-Fe nanoparticles in inner and Co-Pc layers on surface of the spheroids. They showed good characteristics of anti-oxidation and soft magnetic. Increment of ω increased field-induced shear stress and zero-field viscosity (η0) of MR suspensions monotonously, and improved anti-settlement stability, butη0 increased more markedly than with increasing ω. was basically independent on T and γ while increased obviously with increasing H. With increasing T, response time of the MR suspension to external magnetic field seemed to decrease. As a result, MR suspensions with satisfactory stability and rapid, completely reversible and significant MR effect can be obtained from Co-Pc/Fe nanocomposite particles. A novel magnetorheological (MR) suspension was based on methyl silicone oil and cobaltphthalocyanine (Co-Pc) / Fe nanocomposite particles, which were synthesized by decomposing liquid carbonyl Fe in the solution of Co-Pc in N, N-dimethyl formamide. These factors as weight percent of particles (w), magnetic field strength (H), temperature (T) and shear The results indicated that Co-Pc / Fe nanocomposite with density of 3.66 g / cm3 was almost micro-sized regular spheroids consisting of tens of Co-Pc coated α-Fe nanoparticles in inner They showed good characteristics of anti-oxidation and soft magnetic. Increment of ω increased field-induced shear stress and zero-field viscosity (η0) of MR suspensions monotonously, a nd improved anti-settlement stability, butη0 increased more markedly than with increasing ω. was essentially independent on T and γ while increased obviously with increasing H. As increasing than T, response time of the MR suspension to external magnetic field seemed to decrease. As a result, MR suspensions with satisfactory stability and rapid, completely reversible and significant MR effect can be obtained from Co-Pc / Fe nanocomposite particles.