A series of cyanoethylated pullulan (CEP) with various degrees of substitution (DS) were prepared homogeneously, by the addition of a Na/DMSO solution and acrylonitrile to a dimethyl sulfoxide (DMSO) solution of pullulan. The DSs of CEP thus prepared were in the range from 0.045 to 2.89. The CEP with high DSs were soluble not only in dimethylformamide and DMSO, but also in cyclohexanone and acetone. Thermal decomposition temperatures were constant irrespective of the DS. These behavious of the CEPs prepared by the present method were different from those prepared in the presence of water by a conventional method. This suggests that these differences are due to the differences in molecular orientation and distribution of cyanoethyl groups.