An object of the invention is to provide a binder for a separator which can be comprised by a non-aqueous electrolyte battery with improved heat resistance, a separator comprising the binder, and a non-aqueous electrolyte battery comprising the separator. More specifically, provided are a binder for a separator of a non-aqueous electrolyte battery comprising at least a 2-cyanoethyl group-containing polymer having a molecular weight distribution (Mw/Mn), which is a ratio of a weight-average molecular weight (Mw) to a number-average molecular weight (Mn), of 6 or less, the weight-average molecular weight (Mw) of 50,000 to 1,000,000, and 30% by weight or less of a low molecular weight portion having a molecular weight of 30,000 or less.