A method for preserving an organic polymeric material, wherein an organic polymeric material which exhibits strong acidity is preserved with it being dissolved or dispersed in a liquid mainly comprised of water, the method is characterized in that the organic polymeric material is preserved with it being dissolved or dispersed in the liquid so that a concentration thereof is 2 wt %, and a pH (at 25.degree. C.) of the thus obtained liquid is measured and then adjusted so as to be to be higher than the measured pH (at 25.degree. C.). Further, it is preferred that a pH (25.degree. C.) of the liquid before the pH adjustment is 2.2 or lower and a pH (25.degree. C.) of the liquid after the pH adjustment is in the range of 2.5 to 7.5. According to this, even if the organic polymeric material is preserved for a long period of time, it is possible to prevent or reduce a change in a molecular structure thereof with the lapse of time.