Abstract: Three 3,4,5-trimethoxybenzanilide derivatives (Ⅰ_a-Ⅰ_c) and two 3,4,5-trimethoxy-benzamides (Ⅰ_d-Ⅰ_c)were synthesized by condensing 3,4,5-trimethoxybenzoyl chloride with corresponding substituted ethylenediamines. Pharmacblogical tests showed that com-pounds Ⅰ_a, Ⅰ_b and Ⅰ_c exhibited significant antiarrhythmic activity. The therapeutic indices of Ⅰ_a, Ⅰ_b, Ⅰ_c and lidocaine in rats. against aconitine were 7.0, 7.4, 22.6 and 2.6, respectively. The therapeutic doses of Ⅰ_c and lidocaine in dogs against ouabain given intravenously were 10 mg/kg and 18.1 mg/kg respectively.