PURPOSE: To obtain a spinning dope which can be easily spun into a yarn which, when thermally treated, gives a conductive tin oxide fiber by dissolving a tin halide and an alcohol-sol. polymer in an alcohol.

CONSTITUTION: A spinning dope is prepd. by dissolving a tin halide and an alcohol-sol. polymer having a wt.-average mol.wt. of 100,000-5.000,000 in an alcohol. A compd. of a group V element and a silicon alkoxide are added to the dope to improve its conductivity and stabilize its spinning. Pref. tin halides are tin chloride and tin bromide. Any alcohol which dissolves the tin halide can be used, though methyl and ethyl alcohols are pref. because of their high dissolving power. Examples of the polymer are ethylcellulose, cellulose acetate, and polyvinyl butyral. 0.02-0.5mol of the tin halide is dissolved in 1mol of the alcohol followed by concn. by evaporation to adjust the viscosity to a desired value. The amt. of the polymer used is 0.01-20wt.% of the tin halide. The dope can be spun stably even at a high humudity, and the resulting yarn is thermally treated to give a tin oxide fiber.