A magnetic Fe3O4/reduced graphene oxide composite was synthesized by a one-step chemical coprecipitation method and characterized by different methods. The synthesized magnetic composite was used as magnetic sorbent in dispersive solid phase extraction process for preconcentration of 4-tert octylphenol and atrazine. The experimental variables in dispersive solid phase extraction were optimized based on two strategies: one-factor-at-a-time for mixing type and buffer pH; Box Behnken design for sorbent amount, mixing period, eluent volume and buffer volume. Analysis of variance study for proposed model resulted to high determination coefficient (R-2) of 0.957 and adjusted-R-2 of 0.929 indicating a good adjustment of regression model with observed values. Under the optimum extraction conditions, the determination of analytes was carried out by a gas chromatography-mass spectrometry system. The limits of detection and quantification values under the optimum conditions were found to be 1.23 and 4.10 ng mL(-1) for 4-tert octylphenol and 6.81 and 22.71 ng mL(-1) for atrazine, respectively. The low relative standard deviation (<= 6.2%) indicated good repeatability and satisfactory percent recovery values (96.3-112.6%) demonstrated the applicability of proposed method to tap water, river water and waste water samples.