Abstract: Eight title compounds were synthesized in yields of 43.2%~56.5% by chlorination of 1-methoxynaphthalene in CF₃COOH/CH₃COOH mixtures(volume ratio,1:9) at 25℃ with Cl^- as chlorine source, O₂ and catalytic amount of NO⁺ BF₄^- as the oxidant. Their structures were confirmed by virtue of elemental analysis, IR, ¹H NMR and MS. The plant growth regulating activities of the compounds were examined. Most of the compounds have a remarkable plant growth regulating activity, for compounds 6f and 6h the inhibiting activities are -20.3%(6f) and -15.3%(6h) respectively on wheat coleoptile at the concentration of 0.1 g/L, and promoting activities 2.58%(6f) and 2.04%(6h) at the concentration of 0.01 g/L. The inhibition rates of compounds 6a~6h on wheat coleoptile are increased compared with those of 1 hydroxyalkanephosphonic esters (5a~5h) by 2.3%~4.5%, and promotion rates are also increased by 0.24%~0.58%. Chlorine in naphthalene ring appears in favor of improving biological activity of these compounds.