Phthalic acid diamides have received considerable interest in agricultural chemistry due to a novel action mode, extremely high activity against a broad spectrum of lepidopterous insects, low acute toxicity to mammals, and environmentally benign characteristics. A series of phthalic acid diamides (4I-4IV) with the CF3 group at meta position on the aniline ring were synthesized. Their structures were characterized by (1)H NMR and (13)C NMR (or elemental analysis). The structure of N(2)-[1,1-dimethyl-2-(methylthio)ethyl]-3-iodo-N(1)-[3-fluoro-5-(trifluoromethyl)phenyl]-1,2-benzenedicarboxamide (4If) was determined by X-ray diffraction crystallography. Their insecticidal activities against Plutella xylostella were evaluated. The results show that some of the title compounds exhibit excellent larvicidal activities against P. xylostella, and improvement in larvicidal activity requires a reasonable combination of substituents in the parent structure, which provides some hints for further investigation on structure modification.