An organocatalyst-mediated, asymmetric Mannich reaction in the presence of water without using organic solvents has been developed. A highly reactive siloxytetrazole hybrid catalyst has been developed for the reaction of dimethoxyacetaldehyde, while the sodium salt of siloxyproline is an effective catalyst of alpha-imino glyoxylate. Excellent enantioselectivity can be realized, and the usage of organic solvents can be reduced compared to the conventional reactions in organic solvents.