In this study, tin oxide based-dispersive solid-phase extraction (SnO2-DSPE) method followed by flame atomic absorption spectrophotometry (FAAS) was developed for the extraction and sensitive determination of copper at trace levels in domestic and synthetic wastewater samples. Several important parameters including pH and buffer solution volume, adsorbent amount, sample volume, mixing type/period, eluent concentration/volume were optimized to obtain high signal-to-noise ratio and extraction yield for the analyte. Under the optimum SnO2-DSPE-FAAS conditions, a 45-fold enhancement in detection power of conventional FAAS system was achieved by the developed method. Limit of detection (LOD) and limit of quantification (LOQ) values were calculated as 2.9 and 9.6 µg/L, respectively. Recovery experiments were carried out on the spiked domestic and synthetic wastewater samples in order to control the applicability of the developed method. Excellent percent recovery results (74.8–113.3%) were attained for the spiked samples. According to these results, SnO2 nanoparticles synthesized by microwave-assisted method can be used as sorbent material for the preconcentration of copper at trace levels. To the best our knowledge, this is the first study for the preconcentration of copper in wastewater samples by SnO2-DSPE method.