TitrationFit is a program for analyses of metal-ligand or host-guest complexation in solution. This program can calculate the equilibrium constants (association constants) for complexation from the spectroscopic titration data using NMR, UV-vis, etc. This program can be used for the deternimation of various kinds of stoichiometries, not only simple 1:1, 1:2 complexation, but also complicated host-guest system involving host isomerization, dimerization, etc. At present, only a　Japanese version is available.