Ellagic acid (EA) is a naturally occurring polyphenol found in a variety of plants in its free form or in the form of ellagitannin glycosides. In this study, the ellagic acid content of the methanol extracts of Juglans regia L. (Juglandaceae) leaves, Castanea sativa Mill. (Fagaceae) stem bark, and Eucalyptus camaldulensis Dehnh. (Myrtaceae) leaves was determined to develop melanogenesis inhibitors. An improved NaNO2 assay was used for determination of EA. The tyrosinase inhibitory activity of the extracts and synthetic EA was tested in vitro by monitoring the appearance of dopachrome, an intermediate in the melanogenesis process. The results were compared keeping the same total concentration of inhibitor. The efficacy of EA (1%) was compared with arbutin (1%) and hydroquinone monomethyl ether (1%) as reference substances, and it was found to be a more efficient suppressor of pigmentation. The effect of formulation variables on the tyrosinase inhibitory activity was also evaluated. Based on dopachrome tests performed in the formulations, it could be concluded that the combination with plant extracts had a synergistic effect, and gel formulation could be suggested as an effective carrier for treating uneven skin pigmentation.