A solvent extraction separation, preconcentration and determination of thorium with a new crown, 2-ethyl-Nbenzyl-4,7,10,13,16-pentaoxa-1-azacyclooctadecane (MACE), is described in the study. The amount of thorium in the aqueous phase and organic phase was determined by Inductively Coupled Plasma-Optical Emission Spectroscopy and Ultraviolet-Visible, respectively. Thorium loaded organic phase was quantitatively stripped in a stage by using 1.0 M HNO 3 . Thorium was effectively extracted with MACE in the pH range of 6-7 to produce a 3:2 complex ratio in the chloroform. A highly sensitive and rapid spectrophotometric method was described for determination of trace amounts of thorium with MACE. The effective molar absorption coefficient at 281 nm is 1.98 × 10 3 mol −1 cm −1 , and the system complies with Beer's law in the range from 0.464 to 2.32 µg mL −1 of thorium. Thorium was also determined in standard and environmental samples.