Effects of a high magnetic field (with an intensity of 9.4 T) on the cholesteric liquid crystalline structure of ethyl-cyanoethyl cellulose [(E-CE)C] were investigated. The direction of the cholesteric helix axis aligned parallel to the direction of the magnetic field after the (E-CE)C/DCA cholesteric solution was treated in a magnetic field, which indicated that the diamagnetic anisotropy of ethyl-cyanoethyl cellulose molecule is negative. And the correlation between the diamagnetic anisotropy and the molecular structure was discussed. The influence of the magnetic field on the cholesteric order of the (E-CE)C/AA solutions was much smaller than that on the (E-CE)C/DCA solutions, because the pitch in the former system was much smaller than that in the latter one.