5-Aminolevulinic acid (ALA) is a precursor to heme synthesis pathway and currently used to induce endogenous protoporphyrin IX (PpIX, a potent photosensitizer) for photodynamic therapy of cancer. ALA has, however, a limited ability to cross cellular membranes due to its low lipid solubility. The use of lipophilic ALA esters may increase cellular uptake, which results in an enhanced PpIX synthesis. In the present study, a comparison of ALA and its hexyl ester (He-ALA) was made in the QGY human hepatoma cell line with respect to PpIX production and its photocytotoxicity. The fluorescence emission spectrum of the cells incubated with He-ALA was identical to that of PpIX, indicating that He-ALA could induce PpIX in the cells. Fluorescence images demonstrated that the He-ALA induced PpIX was localized in the cytoplasm of the cells. Moreover, a similar amount of Pp IX was found in the cells incubated with 0.2 mmol/L He-ALA or 2 mmol/L ALA and a similar level of cell survival was reached following light exposure. These results suggest that He-ALA is much more efficient at producing PpIX and photocytotoxicity than ALA itself in the cells.