After sprouting of onions, the shoots are used as vegetables and bulbs discarded. These usually discarded onion bulbs may have improved antioxidant potentials resulting from sprouting. These improved properties could be harnessed to combat or manage some degenerative and non-communicable diseases. This study was therefore conducted to determine the effects of sprouting on the antioxidant potentials of onions (Allium cepa L.). Samples were sprouted for 0–10 days. Phytochemical (total phenols, flavonoids, ascorbic acid) analyses and antioxidant activities such as reducing power, DPPH and ABTS radicals scavenging activities were used to assess antioxidant potentials using standard methods. The results show that a significantly (P< 0.05) higher total flavonoid content was expressed in methanol extract of onions sprouted for eight days (7.84 mg/g RE). Generally, sprouting for 2–8 days resulted in a significant (P< 0.05) increase in all the antioxidant parameters tested. This was followed by a slight but significant decrease at the 10th day of sprouting. The present study shows that sprouted onions demonstrated higher antioxidant activity and can be considered as good sources of natural antioxidants.