A photographic image coupler is studied in this paper for its solution-mediated transformation from metastable polymorph I to stable polymorph II. Solubilities of two polymorphs in an organic solvent were measured using an ultraviolet-visible spectrometer through a range of temperatures. Dissolution behaviours of two polymorphs were investigated over time. The solution-mediated transformation was found to occur with the dissolution of metastable polymorph I and the growth of stable polymorph II. The kinetics of the transformation were described with the model developed by Cardew and Davey.