Abstract: The p-, o-and m-trifluoromethyl-substituted cinnamamides were synthesized. Their trans-configurations were verified by NMR and IR. The anticonvulsant activity was tested by MES. The results showed that the introduction of p-and m-CF₃ groups led to products with higher anticonvulsant activity. The Hammett constant of p-CF₃ group is higher than that of m-CF₃ group. It was originally expected that the activity of p-trifluoromethyl cinnamamides should be higher than that of m-trifluoromethyl compounds. But the results showed that the anticonvulsant activities of both compounds were not significantly different. The steric effect of o-CF₃ group was also demonstrated in UV spectra. This steric effect exerts its influence on the resonance between the benzene ring and the ethylenic double bond, and decreases the anticonvulsant activity of the compound.