A simple, quick and environmentally friendly microwave-assisted synthesis method was developed to produce MoS2 nanoparticles (MoS2NP) for the preconcentration of thallium. The characteristics of the synthesized MoS2NP were validated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The determination of thallium was achieved with MoS2NP based preconcentration and a flame atomic absorption spectrophotometer (MoS2NP-PM-FAAS). A detection limit of 14.6 µg/kg was achieved for thallium using the optimum conditions by the MoS2-PM-FAAS method. The developed method provided an improvement in the detection power of the FAAS system by approximately 20-fold. The applicability of the method was validated with tea samples through spike recovery experiments.