The aim of this study was to estimate the phenolic composition and xanthine oxidase (XO) inhibitory activity of green coffee beans (GCB) and wholemeal wheat flour (WF). Additionally, the type and strength of interaction (expressed as the combination index, CI) and mode of XO inhibition were analyzed. The major phenolic in GCB was 5-caffeoylquinic acid (39.92 mg/g dw). The main phenolic acids in WF were trans- and cis-ferulic acids (257 and 165.57 mg/100 g dw, respectively). Both ferulic and chlorogenic acids individually inhibited XO, and for their combination moderate synergism was found. Buffer extractable compounds from GCB and WF demonstrated slight synergism (CI = 0.92), while potentially bioaccessible and bioavailable compounds acted synergistically (CI = 0.43 and 0.54, respectively). Buffer-extractable and potentially bioavailable phytochemicals from GCB acted uncompetitively, whereas potentially bioaccessible compounds acted as noncompetitive XO inhibitors. The addition of 3–5% of GCB to wheat bread significantly increased XO-inhibitory activity.