The present research aimed at evaluating the effect of drying on the antioxidant properties of three varieties of onion. Onion powders were prepared after solar or electric dryings. The total phenolic compounds (TPC), flavonoids, tannins, and vitamin C were assayed at time in the fresh and powdered samples of these varieties. The total reducing power (TRP) and scavenging capacity (ABTS and DPPH) were also evaluated. Results showed a significant decrease (P _ 0.05) in the parameters evaluated during drying and a significant positive correlation (P _ 0.05) between ABTS and DPPH (R2 = 0.602) and between TPC and TRP (R2 = 0.77), and between TPC and the scavenging capacity (R2 = 0.88, R2 = 0.71 for ABTS and DPPH respectively). The Violet of Galmi variety appeared to have the strongest antioxidant activity even after drying. In general, drying reduced the antioxidant activity of onion.