Introduction: It was shown in cell cultures of different malignomas that chloroquine results in an increased apoptosis rate. Therefore current research evaluates this agent alone or in combination with other therapeutics for treatment of these malignant diseases. The aim of this study was to analyze the effect of chloroquine on the viability and apoptosis rate of squamous cell carcinoma (OSCC) in-vitro. Materials and Methods: Cells of the tumor cell lines PCI1 and SCC68 were incubated for 24h with increasing concentrations (10, 30 and 50μg/ml) of chloroquine. Untreated tumors cells were used as controls. Apoptosis rate was evaluated by fluorometric determination of the activity of caspase 3 and 7. The viability of the tumor cells was checked by WST-assay. All tests were conducted at least five times. For statistical analysis a student's t-test was performed at a significance level of 5%. Results: The in vitro study shows a dose -dependent degradation of the cell viability for both tumor cell lines: (PCI1: 0µg/ml: 100%; 10µg/ml: 77%; 30µg/ml: 65%; 50µg/ml: 60% [p=0,01, for control versus 50µg/ml]; SCC68: 0µg/ml: 100%; 10µg/ml: 62%; 30µg/ml: 39%; 50 µg/ml: 21% [p0,001, for control versus 50µg/ml]). Corresponding to this are the results from the caspase assays with a concentration dependent increase in apoptosis rate compared to the untreated control cells (PCI1: 10µg/ml: +46%; 30µg/ml: +160%; 50µg/ml: +220% [p=0,006, for control versus 50µg/ml]; SCC68: 10µg/ml: +195%; 30µg/ml: +329%; 50µg/ml: +330% [p=0,002, for control versus 50µg/ml]). Conclusions: The incubation of the OSSC cells with chloroquine resulted in a dose-dependent degradation of the cell viability and consecutive increase of the apoptosis rate. Therefore, Chloroquine could potentially be useful for the therapy of the OSSC which has to be evaluated in further in vitro and in vivo studies. Keywords: Squamous cell carcinoma, therapy, chloroquine