Provided are a sizing agent for quartz glass fibers capable of suppressing charging of quartz glass fibers, and suppressing generation of fluff in a production process for quartz glass fibers and a weaving process for a quartz glass cloth, a quartz glass fiber or a quartz glass yarn having applied thereonto the sizing agent, a quartz glass cloth, a prepreg for a printed circuit board, and a product using the quartz glass fiber. The sizing agent for quartz glass fibers includes an aqueous solution containing: a cationic vinyl acetate copolymer emulsion in which a cationic vinyl acetate copolymer having a weight average molecular weight of from 5,000 to 500,000 is dispersed in water; and starch, in which emulsion particles of the cationic vinyl acetate copolymer emulsion have a 50% diameter on a volume basis of from 0.1 μm to 5 μm.