The quantification of hydrogen peroxide (H2O2) generated in the plasma-liquid interactions is of great importance, since the H2O2 species is vital for the applications of the plasma-liquid system. Herein, we report on in situ quantification of the aqueous H2O2 (H2O2aq) using a colorimetric method for the DC plasma-liquid systems with liquid as either a cathode or an anode. The results show that the H2O2aq yield is 8-12 times larger when the liquid acts as a cathode than when the liquid acts as an anode. The conversion rate of the gaseous OH radicals to H2O2aq is 4-6 times greater in the former case. However, the concentrations of dissolved OH radicals for both liquid as cathode and anode are of the same order of tens of nM.