Basalt fiber (BF) is a promising material for 2,2'-bis(4-cyanatophenyl)isopropylidene reinforcement that is cost effective and has a low dielectric constant. In this study, BF was impregnated with lanthanum-ethylenediaminetetraacetic acid (La-EDTA) to improve its mechanical and interfacial properties. The properties of the La-EDTA BF and pristine BF were compared using X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy to reveal the modification mechanism. The results confirmed that La-EDTA was successfully introduced on the BF surface as a crystalline lanthanum dihydrate via the reaction between various oxides and the -COOH group of La-EDTA. Moreover, the structure-property relationship of the La-EDTA BF was investigated by performing tensile strength and contact angle tests of BF monofilaments. The results showed that the average BF monofilament fracture load increased from 124.03 mN to 163.29 mN after modification; further, the contact angle between BF and 2,2'-bis(4-cyanatophenyl)isopropylidene decreased at 200 degrees C due to chemical compositional changes on the BF surface. This study confirms the applicability of La-EDTA BF as a reinforcement for BADCy composites.