A fiber masterbatch including a polyetherimide, a polyethylene terephthalate, and a polyimide is provided. A glass transition temperature of the polyimide is between 140° C. and 170° C., a 10% thermogravimetric loss temperature of the polyimide is between 500° C. and 550° C., and when the polyimide is dissolved in N-methyl-2-pyrrolidone and a solid content of the polyimide is 15 wt %, a viscosity of the polyimide is between 80 cP and 230 cP. A melt spun fiber obtained by using the fiber masterbatch is also provided.