NEW MATERIAL:A S-aroylthiooxime of formula I (Ar is aryl which may have a substituent; R is phenyl or heterocyclic group which may have a substituent at the p-position). EXAMPLE:S-Benzoylbenzthiooxime. USE:The compound exhibits a SHG activity and useful as a nonlinear optical material. Since the compound exhibits high reactivity and reacts with various kinds of reagents to give many derivatives, the compound is useful also for synthetic chemistry. PREPARATION:A S-aroylsulfenamide of formula II is reacted with an aldehyde of formula III in the presence of an acid catalyst in an organic solvent at 50-100 deg.C to provide the component of formula I. The compound of formula II is synthesized by dropping a hydroxylamine-O-sulfonic acid aqueous solution into the alkali aqueous solution of an aromatic thiocarboxylic acid at a temperature below room temperature.