[en] Solvent extraction studies were carried out for the selective separation of thorium from uranium which is important for Indian nuclear programm. In this study we have used an acidic extractant, a Pyrazolones, HPMBP(1- phenyl- 3- methyl 4- benzoyl pyrazolone-5) which have a lower pK value of around 4.2. In this connection some basic studies on the extraction of thorium were carried out. Equal volumes of aqueous solutions of thorium and HPMBP were equilibrated and phases were separated. After centrifugation, from the aqueous phase known volumes were withdrawn and absorbance values were measured by spectrophotometric method using arsenazoIII as chromogenic reagent against corresponding blank. Absorbance of original thorium solution was also measured in the same way. From the absorbance value of aqueous thorium solution before and after equilibration the absorbance due to thorium extracted into the organic phase was found out by difference