The present study was designed to determine the composition of the essential oil of Eucalyptus camaldulensis Dehnh. leaves and to examine its in vitro antioxidant and antidiabetic activities. The chemical composition of the essential oil from Eucalyptus camaldulensis Dehnh. leaves was analyzed by GC/GC-MS, twenty-nine compounds representing 99.10% of the total oil were identified. The major components of the oil were p-cymene (68.43%), 1,8-cineole (13.92%), 1-(S)-α-pinene (3.45%) and R-(+) limonene (2.84%). The antioxidant features of the essential oil were evaluated using inhibition of 2,2-diphenyl-1-picrylhydrazyl, hydroxyl, and superoxide radicals, inhibition of hydrogen peroxide and lipid peroxidation assays. We also studied α-amylase and α-glucosidase inhibition in vitro to assess the antidiabetic properties of the essential oil. Both α-amylase and α-glucosidase were inhibited by a non-competitive mechanism.