A process for producing tertiary amine oxide having two methyl or ethyl groups and one long chain primary aliphatic group in a stable, solid form is described. Aqueous 65-90% hydrogen peroxide and tertiary amine having two methyl or ethyl groups and one primary aliphatic hydrocarbyl group of 8-24 carbon atoms are mixed in proportions of ca. 1.1-1.3 moles of hydrogen peroxide per mole of tertiary amine in the presence of carbon dioxide and in the absence of organic solvent. When the conversion of the tertiary amine to tertiary amine oxide in the reaction mass has reached ca. 60-90%, the reaction mass is transferred to a separate vessel and the reaction mass is then allowed to solidify at a temperature of ca. 20-60.degree. C. The process makes possible the production of highly pure solid product without formation of any appreciable amounts of undesirable by-products. Also, the process is environmentally friendly, and the problems and expense associated with product workup, purification, crystallization, and waste product disposal are largely, if not entirely, avoided. Moreover, the solid storage stable products can be stored and shipped at significantly reduced costs as compared to liquid solutions. The products are useful in the manufacture of household and commercial laundry detergent formulations furnished in the form of powders or flakes.