Tris(hydroxymethyl)methyl ammonium salts, [C(CH₂OH)₃NH₃]X, were obtained for the first time by the interaction of tris(hydroxymethyl)aminomethane (TRIS) with carboxylic acids (cinnamic, benzoic, salicylic, nicotinic, 2-methylphenoxyacetic, succinic, malonic, oxalic, malic and citric). The new compounds (1–15) were characterized by ¹H NMR, ¹³C NMR, FT-IR, elemental analysis and thermal analysis methods. The crystal structures of the tris(hydroxymethyl)methyl ammonium hydrogen malonate, hydrogen succinate and 2-methylphenoxyacetate were determined by the single-crystal X-ray diffraction. The antimicrobial activity of some synthesized tris(hydroxymethyl)methyl ammonium salts against bacteria Escherichia coli, Staphylococcus aureus, Mycobacterium tuberculosis and fungi Candida albicans and Aspergillus niger has been investigated.