2-(5,7-Difluoro-3-indolyl)propionic acid (5,7-F₂-IPA, 1) and 2-(5,7-difluoro-3-indolyl)isobutyric acid (5,7-F₂-IIBA, 2) were synthesized from 5,7-difluoroindole-3-acetic acid (5,7-F₂-IAA). N-Protected 5,7-F₂-IAA methyl ester was lithiated followed by monomethylation to give carbamate ester (8); direct double hydrolysis of 8 produced 5,7-F₂-IPA, and remethylation plus subsequent double hydrolysis of 8 gave 5,7-F₂-IIBA. Bioassays with Avena coleoptiles showed 5,7-F₂-IPA had stronger auxin activity than IAA and no growth inhibition. 5,7-F₂-IIBA exhibited weak auxin activity at concentrations <3×10⁻⁶ M and antiauxin activity at >1×10⁻⁵ M; its inhibitory activity was slightly weaker than 5,7-Cl₂-IIBA but much stronger than PCIB.