Influence of extraction temperature (90-180 °C), solvent concentration (36-90% ethanol) and time (30-90 min) on extractability of phenolic compounds from barley grains and on antiradical power of extracts was examined. Response surface methodology (RSM) was used to design and optimize the processing parameters. Experimental results of total phenolic contents, total flavonoids, and antiradical power of barley extracts were in the range from 3.27-26.60 mgGAE/gdb, 0.91-6.09 mgCE/gdb and 0.33-4.05 mgDPPH/mLext, respectively. HPLC analysis of extracts showed epigallocatechin gallate to be the predominant phenolic compound, representing up to 93% of all phenolic compounds determined. Based on RSM analysis, temperature was the most significant factor affecting the observed responses (p < 0.05) and optimal extraction conditions were achieved at 180 °C, 36% ethanol and 90 min. Additionally, strong correlation between proteins content and phenolic compounds of extracts was observed (R = 0.925), indicating influence of total proteins on possible overestimation of polyphenol content.