In this paper, the effects of ultraviolet (UV) treatments on the aloin content of Aloe vera L. gel have been analyzed. UV-A treatment to A. vera plants for 36 days led to an increase in the aloin concentration in gel, rind tissue, and latex, while a decrease in chlorophylls a and b occurred in the photosynthetic tissue as a consequence of UV treatment. The growth of Penicillium digitatum and Botrytis cinerea (artificially inoculated on the leaf surface) was drastically decreased in UV-A-treated leaves, which could be attributed to the increase in the aloin concentration by the UV-A treatment. In addition, UV-C treatment to detached leaves also led to an increase in the gel aloin concentration, at higher levels than occurred with UV-A treatment, although leaves showed severe lesions after 48 h of treatment.