A quick, simple and environmentally friendly liquid phase microextraction (LPME) sample pretreatment procedure was proposed based on pH-switchable hydrophobic deep eutectic solvents (HDESs) and high performance liquid chromatography coupled with a fluorescence detector (HPLC-FL). This method was used for the quantitative study of aflatoxin B1 (AFB1) and applied to eight widely consumed cereal samples. In this method, six different DESs were synthesized and then their pH-switchability was investigated. DESs that could be switched with pH were employed for separation and preconcentration of AFB1 in cereal samples. In this method, dispersing the extractant phase in the aqueous solution and subsequent phase separation are performed only by changing the pH. Important parameters affecting extraction, such as the type of DES and its volume, concentration of KOH, volume of HCL, effect of salt and extraction time were investigated and optimum conditions were obtained. Under the optimum conditions, relative standard deviation (RSD) values for intra-day and inter-day of the method based on seven replicate measurements of 5.0 μg kg-1 of AFB1 in cereal samples were 3.3 and 5.2%, respectively. The calibration graphs were linear in the range of 0.007-20 μg kg-1 and limit of detection (LOD) was 0.002 μg kg-1. The relative recoveries of real cereal samples which have been spiked with different levels of AFB1 were 90.8-107.5%.