Chloromethylisopropylphenois, namely 4-chloro-3-methyl-2-isopropyl phenol, 4-chloro-3-methyl-5-isopropyl phenol and their 6,6'-methylene and 2,2'-methylene bis derivatives, effective as a bactericide and fungicide, especially against staphylococcus, pneumococcus and tricoccus. They are effective in doses as low as 5 ppm, are stable, substantially odor-free and can be readily prepared by conventional chemical reactions to obtain a substantially nontoxic white product.