Two short, straight alkyl chain substituted dithiophosphinic acids were investigated as extractant candidates for actinides (An) and lanthanides (Ln) separation. The extraction and separation performance by di-n-pentyl dithiophosphinic acid for Am3+ and Eu3+ was very attracrive and comparable to Cyanex 301. The radiation effect on Am3+ and Eu3+ extraction of di-n-pentyldithiophosphinic acid was investigated. The chemical stability and radiation stability of the two dithiophosphinic acids were also examined. Di-n-pentyldithiophosphinic acid which is of 35% higher gravimetric An loading than purified Cyanex 301 was proven a potential candidate for industrial-scale An and Ln extraction separation.