PURPOSE: To compose and ink evaporation and outflow prevention body for an aqueous ball point pen of specified viscosity by using at least one hard-to- volatilize liquid selected from phthalic ester plasticizers as a base and blending the composition with an alicyclic saturated hydrocarbon resin and fine particle silica as a thickening agent.

CONSTITUTION: A composition 1 of ink evaporation and outflow prevention body is used for an aqueous ball point pen filled with aqueous ink 2 having the viscosity of 30-1500 cps at 25°C in a transparent or a translucent ink storage tube composed of polyethylene or polypropylene. The composition of ink evaporation and outflow prevention body is composed of one at least one hard-to- volatilize liquid (example: phthalic dimethyl) selected from phthalic ester plasticizers as a base blended with an alicyclic saturated hydrocarbon resin (example: Alcon p-70) and fine particle silica as a thickening agent. As a result, the composition shows the superior effect for the evaporation and outflow prevention.