There is provided a lubricant for hot plastic working, which contains 20 to 40 mass % of iron oxide and 10 to 30 mass % of sodium silicate, wherein impurities are 3 mass % or less, and the lubricant contains 40 to 60 mass % of water. By virtue of combined action of these components, the lubricant exhibits excellent lubricity and suppliability and does not adversely affect the corrosion resistance of product. The lubricant is suitably used for lubricating a guide shoe in piercing-rolling, for example, a high-Cr steel and achieves a great effect of preventing a seizure flaw from occurring on the outer surface of product by being applied directly to the outer surface of a workpiece just before piercing rolling, preferably, within one second before starting piercing rolling.