This invention relates to a water-soluble lubricant for warm or hot metal forming, comprising a high polymer compound which comprises an imide group, which has a weight-average molecular weight of from 1,000 to 1,000,000. The water-soluble lubricants of the invention possess exceptional lubricity for reducing friction between a die and a workpiece, have a minimal adverse effect on the operating environment, and can readily be treated in wastewater.