Isosaccharinic acid (ISA), a degradation product of cellulous materials, has been a subject of study due to its presence in cellulose co-disposed low-level nuclear wastes and its ability to complex actinides. Because ISA itself is biodegradable, it has been proposedto incorporate ISA into foams for the purpose of cleaning contaminated surface, replacing complexants that are harsh to the natural environment. In this work, the complexation of isosaccharinic acid with Th(IV), U(VI) and Np(V) has been studied at 25 oC. Formation constants of the complexes and the enthalpy of complexation were determined by potentiometry and calorimetry, respectively. To help evaluate the effectiveness of ISA for decontamination in the presence of common competing ions, the complexation of ISA with Fe(III) and Ca(II) was also investigated.