An on-line solid-phase extraction (SPE) following a liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method was established for the simultaneous analysis of bisphenol A (BPA), nonylphenol (NP), and octylphenol (OP) in cereals (including rice, maize, and wheat). The target compounds were extracted by acetonitrile, purified by an automated on-line SPE cartridge, and analyzed by LC-MS/MS under the negative-ion mode. Mean recoveries fortified at three concentration levels ranged from 81.6 to 115.7%, and the coefficient of variation ranged from 4.6 to 19.9% (n = 6). The limits of quantification (LOQs) of the method were 0.5, 0.5, and 0.25 μg/kg for BPA, NP, and OP, respectively, in both rice and maize, while the LOQs in wheat were 0.5, 1.25, and 0.5 μg/kg for BPA, NP, and OP, respectively. This method was applied in the analysis of rice, maize, and wheat from a local market. As a result, NP occurred in all cereal samples at the concentration range of 9.4-1683.6 μg/kg and BPA was detected in a few samples.