A new green method was developed for the quantification of paraquat (PQ) in water samples based on the fluorescence emission enhancement of the herbicide signal after adsorption on sodium montmorillonite clay (MMT). Radiant emission processes are favored by increasing the molecular rigidity of the PQ since it adopts a planar position between the nano-sheets of the MMT. The advantages of the use of this clay are nontoxic, low cost and found in abundance in natural reserves. The proposed method was successfully used in determining PQ in natural water samples with recoveries of 73% to 95%. The fluorescence emission showed a good linear relationship with PQ concentrations from 2.0 to 8.0 μmol L⁻¹ with a detection limit of 0.37 μmol L⁻¹. The method is simple, inexpensive and does not require the use of reagents or organic solvents; which makes it very promising to achieve the goals of green chemistry. The proposed methodology could be the beginning of the development of future green sensors.