A validated spectrophotometric method has been described for the determination of thorium(IV) in synthetic mixture and soil samples. The method is based on the complexation of thorium(IV) with rifampicin at room temperature which absorbs maximally at 525 nm. Beer's law is obeyed in the concentration range 1.16–23.2 μg mL−1 with apparent molar absorptivity and Sandell's sensitivity of 8.23 × 103 L mol−1 cm−1 and 0.0232 μg/cm2/0.001 absorbance unit, respectively. The influence of variables was investigated and optimized. Interference due to other metal ions was studied and the tolerance limit was achieved. The proposed method was applied to the analysis of thorium(IV) in a synthetic mixture containing various other metal ions and in soil samples. The results of analyses of the proposed method were statistically compared with the reference method showing acceptable recovery and precision.