This study was aimed to modify xanthorrhizol from Curcuma xanthorrhiza Roxb via dimerization process using peroxidase enzyme from raw extract of broccoli as catalyst. This experiment was carried out via several steps, as follows: extraction of xanthorrhizol from curcuma, extraction of peroxidase enzyme from broccoli, dimerization process of xanthorrhizol, characterization of products. The results showed that the extraction of curcuma using ethyl acetate produce viscose liquid with Rf 0.4 which was predicted as xanthorrhizol. In the further step, this extract was dimerized using peroxidase enzyme extracted from broccoli and produced a substance which expected to be a new compound since there was a moderate shift in wavelength at UV region. FTIR spectrum confirmed the breaking of the benzene ring and the formation of ketone group. The antioxidant assay using DPPH method revealed the increase of IC₅₀ from 467.5 ppm to 578.9 ppm (withoutTween-80) and 1056.6 ppm (withTween-80).The result of antimicrobial assay showed that thatdimerization product have higher inhibition power than the unmodified xanthorrhizol extract, against the growth of Bacillus cereusatconcentration of0.2-0.8% with inhibition power of 8-14 mm (moderate to strong), but could not inhibit the growth of E.coli and some fungies (Pestalutiopsis, Penicilium and Aspergillus niger) in the concentration range of 0.2 – 1%.