an anionic surfactant powder prepared by subjecting a mixture of an anionic surfactant and a solvent to microwave irradiation to remove at least a part of the solvent , and a process for preparing the anionic surfactant . the anionic surfactant powder can be suitably used for laundry detergents , detergents for tableware and kitchenware , foaming agents for toothpastes , powdery shampoos , emulsifying agents for polymerization , foaming agents for cement plaster and the like .