Aloe vera L. is a valuable medicinal plant and is currently used in pharmaceutical, cosmetic, and food industries worldwide. In the present study, the effect of various concentrations of Aloe vera leaf gel extracts was investigated on mitotic and phase indexes of Allium cepa L. root tip cells for 24 and 48 h durations. The EC50 value of gel extracts was found to be 20% and was used to determine the experimental concentrations. The results indicated that the mitotic index and root growth rate of A. cepa were considerably decreased in comparison to the control. We found that the cytotoxic effect of A. vera gel extracts depends on the concentration rather than the exposure time. Even the low doses caused a considerable decrease in root growth rate. The lowest mitotic index value was found to be 3.72% at 40% gel extract treatment for 48 h duration. Average prophase index during 24 and 48 h applications was found to be 53.80% and 56.48%, respectively. We conclude that A. vera gel extracts have a cytotoxic effect on the root tip cells of A. cepa.