Abstract: MTT assays is adopted to study of proliferation inhibiting effect of four kinds of alkyls trimethyl ammonium chloride and three kinds of alkyls dimethyl benzyl ammonium chloride on HeLa cells and CHO cells , and to discuss cytotoxicity of two kinds of cationic surfactants which are structurally related. The results indicated that the proliferation inhibiting effect of alkyls trimethyl ammonium chloride and alkyls dimethyl benzyl ammonium chloride on both HeLa cells and CHO cells gradually increased with con-centration increased；Proliferation inhibiting effect of Both these two kinds increased with the number of carbons increased.Cytotoxi-city of alkyls trimethyl ammonium chloride is lower than alkyls dimethyl benzyl ammonium chloride.

Key words: alkyl trimethyl ammonium chloride, alkyl dimethyl benzyl ammonium chloride, CHO cells, HeLa cells, MTT-assay, proliferation inhibition