Abstract: Based on the previous paper^[1], the activity coefficients f₂ of TBP in n-amyl acetate, methyl cyclohexanone, n-C₈H₁₇OH, n-C₈H₁₈ have been determined by ³²P-labled TBPdistribution method. These activity coefficients may be described by the following equations. lgf₂=aN₁² and lgf₂ =A/(1+By)₂, where y = N₂/N₁,N₁ and N₂ are molfractions of solvent and TBP, and constants a, A, Bwere obtained by graphical method. The effect of different solvents on the activity coefficients has also been discussed.