PURPOSE: To profitably prepare an organic sulfonic acid metal salt useful as an anionic surfactant without water or any organic solvent by neutralizing a long chain organic sulfonic acid with a specific neutralizing agent.

CONSTITUTION: A long chain organic sulfonic acid such as an organic sulfonic acid or higher alcohol sulfate having a 8 to 18C long chain portion is neutralized with a solid powdery metal carbonate salt or bicarbonate salt or a mixture thereof as a neutralizing agent to prepare a long chain organic sulfonic acid metal salt. The neutralizing agent has preferably a suitable small size, e.g. a particle size range of 30 to 700μm. The un-employment of water or an organic solvent necessitates no drying process and the addition of the long chain organic sulfonate metal salt to a builder, filler or any other filler as such permits to automatically and continuously provide a detergent product in one step, thereby allowing to save energy, save spaces for the production of the detergent product and improve the efficiency of the production.