Abstract: It was found that nanoparticles of α-FeOOH/GO, prepared by ultrasonic in situ precipitation, behaved to have the activity mimetic to HRP and to catalytically activate H2O2, by which the base compound, N,N-diethyl-p-phenylenediamine was oxidized to give a colored compound with absorption maximum at 550 nm. Under the optimized reaction conditions. Linear relationship between values of absorbance and concentration of H2O2 was obtained in the range of 2.0×10-7-2.0×10-4mol·L-1, with detection limit (3S/N) of 1.0×10-7mol·L-1. Based on these facts a rapid spectrophotometric method for determination of H2O2 was proposed. The proposed method was applied to determination of H2O2 in samples of rainwater and honey. Recovery was tested by standard addition method, giving results of recovery in the range of 92.3%-108%, with values of RSD′s (n=5) less than 5%.