To obtain a binder for forming a glass fiber having little naps and excellent in running stability and degreasing ability through heating, by making the binder contain a specific amount of a dextrin and/or an oligosaccharide to a starch, which is a main film-forming material.

This binder for glass fibers contains 0.1-10.0 wt.% of a dextrin and/or an oligosaccharide based on a starch, which is a main film-forming material. The dextrin and the oligosaccharide are used by adding to the binder or generating the dextrin and the oligosaccharide during processing of starch. A preferable ratio of the dextrin and/or the oligosaccharide to starch is 0.5-8.0 wt.%. E.g. a starch glue solution is prepared by mixing 100 pts.wt. of hydroxyalkyl etherified starch with 1 pt.wt. of roast white dextrin, dispersing the mixture in 10 times of water, raising the temperature by heating, heating at 95°C for 30 minutes and cooling to 60°C.