Abstract: In this paper the ligand exchange rate constants (Kr) and thermodynamic functions of activated complexes △G++, △H++, △S++, Ea for DMHMP-UO2(NO3)2 and DRRP-UO2(NO3)2 systems have been determined by NMR method. It is found that for both systems the activation energies Ea are approximately 6 . 50-7 . 88 kcal/mol, which shows that the exchange rates are rather high. From the rate constant expression derived from transitionstate theory, Kr=KT/he △S++/R·e-Ea/RT, it can be seen that the influences of Ea aswell as △S++ on rate constant of the exchange reaction Kr are considerable. Thus the Kr values in various systems reported in this paper are comprehensive results which show the effect of Ea and △S++.Since the free entropy of activation △S++ for these two systems are about -23.6-- 28.3 cal/mol·K, which is nearly the same as the free entropy of activation for TBP-UO2 (NO3)2 system4, it indicates that the exchange reactions of both systems should belong to association mechanism according to the exchange reaction mechanism. From DRRP-UO2 (NO3)2-HNO3 system it can also be seen that the free energy of activation △G++ is increased with increasing HNO3 concentration in the system. It might be explained that HNO3 is extracted by DRRP and the hydrogen bond with the phosphoryl group ( P=O) in DRRP is formed due to the increase in HNO3 concentration.