A polycyano aryl ether which has recurring units each represented by the formula: ##STR1## and a reduced viscosity of which is 0.3 dl/g or more at 60.degree. C. in a solution in which the polycyanoaryl ether is dissolved in p-chlorophenol in a concentration of 0.2 g/dl.A method for preparing the above-mentioned polycyanoaryl ether which comprises reacting a dihalogenobenzonitrile represented by the formula: ##STR2## wherein X is a halogen atom, with an alkali metal salt of dihydroxynaphthalene represented by the formula: ##STR3## wherein M is an alkali metal, in the presence of a solvent.And a method for preparing a polycyanoaryl ether powder without mechanical grinding steps for purification, which comprises adding to the resulting reaction mixture of the above-mentioned polycondensation reaction a solvent which does not dissolve the resulting polymer but has compatibility with the solvent used in polycondensation when the concentration of the resulting polymer dissolved in the resulting rection mixture reaches to the range of from 2 to 20% by weight.The polymer of this invention is excellent in mechanical strength, fire retardance and solvent resistance. Further, the method of this invention can prepare the high molecular weight polycyanoaryl ether with ease and with high productivity when compared with a conventional method. Moreover, if the method for preparing the polycyanoaryl ether powder of this invention is applied, a mechanical process for grinding the resulting polymer will be unnecessary, the powder prepared by this invention is finer than the conventionally pulverized powder and the subsequent purification process is carried out to a sufficient degree.