To obtain a fiber sizing agent for pre-wet sizing capable of exhibiting sufficient weaving properties without destroying a size film by abrasion, etc., on a loom because an excellent cohesive force is exhibited even in a state of the sizing agent sticking only to the vicinity of the surface layer by the pre-wet sizing.

This fiber sizing agent for pre-wet sizing comprises a PVA containing 0.1-20 mol% of an ionic group-containing monomer unit.