Millet is a grass that responds to potassium fertilization and Verdete and Thermopotash are potential sources of this nutrient. This study was carried out to evaluate the potential of verdete rock and thermopotash as potassium sources by measuring K accumulation by millet grass crop. The millet was grown in Ustoxic Quartzipsamment (RQo) soil. The experiment was set up in randomized block design with three replications. The treatments consisted of three K sources (KCl, thermopotash and verdete rock), two K rates (200 and 400 kg ha^-1 K₂O) and the control.  Two consecutive of millet crops were grown in the same pots. The first crop received potassium source application but not the second. At the end of experiment, shoot dry matter production, shoot potassium concentration, shoot accumulated potassium, soil potassium and agronomic efficiency were determined. The agronomic efficiency, calculated based on both crops, was 84 % for thermopotash and was 11% for verdete rock. Millet was able to absorbed potassium from the thermopotash source in both, first and second crop.