The invention is directed to a method for producing a fatty acid salt, the method comprising reacting a fatty acid with a metal oxide or a metal hydroxide by use of an extruder having at least a stock supply zone, a kneading/reaction zone, and a cooling zone. The invention provides a high- productivity, highly efficient method for continuously producing a fatty acid salt and a method for effectively producing a fatty acid salt having a high unsaturated fatty acid content and a low melting temperature.