A process for preparing 2-hydroxy-4-methylthiobutyric acid ammonium salt involves reacting 3-methylthiopropionaldehyde with hydrogen cyanide to form 2-hydroxy-4-methylthiobutyronitrile, and subsequently hydrolyzing the 2-hydroxy-4-methylthiobutyronitrile by catalytic hydrolysis to form the ammonium salt of the 2-hydroxy-4-methylthiobutyric acid in a single process step. One catalyst may be used in the hydrolysis for the whole reaction. The catalyst is preferably a solid containing a titanium compound such as, e.g., titanium nitride, titanium sulfide or titanium dioxide. The 2-hydroxy-4-methylthiobutyric acid ammonium salt produced by this process is nutritional and can be used as an additive in feedstuffs.