A process for preparing As.sub.4O.sub.6 comprises successively heating and cooling a mixture of natural Sinsuk and 40% alcohol in a ratio of about 1: about 1 for about 1 to about 2 hour(s) resulting in a product, successively washing the product with distilled water thereby forming washed precipitates, maintaining the washed precipitates at about -40.degree. C. for 24 hours, defrosting, filtering, and drying the precipitates, and successively heating and cooling the precipitates to obtain the final As.sub.4O.sub.6 product.