In general, consumers associate vegetable quality to external appearance. For onions, parameters such as bulb size, color, aroma, taste, firmness and chemical composition are the most important. These characteristics are determined by the genotype, by pre and post-harvest treatments and by the appropriate harvest season. Curing is an important process for ensuring post-harvest quality of onions by removing excess moisture from the outer layers of the bulbs and roots before storage. The objective of this work was to determine the effect of curing on the bioactive compounds content and antioxidant capacity of onions of 'BR-29' and 'Perfecta' cultivars. The cultivation was carried out between July and December of 2016, in the organic vegetable area of the Experimental Station Center of Canguiri / UFPR and harvest was carried out in December 2016. During the curing process, the onions were kept in an oven at 28 °C for three months. After this period, the bulbs were oven dried at 65 °C and powdered for determination of: total phenolics using Folin-Ciocalteau’s reagent; total flavonoids, by reaction with aluminum chloride; and antioxidant activity, using DPPH radical. The curing process reduced total polyphenol content by 63% in 'BR-29', but did not cause changes in 'Perfecta' cultivar. No effect of curing on the flavonoid content of the cultivars was observed. The antioxidant activity before curing varied from 72 to 82% inhibition of the DPPH radical in the cultivars 'Perfecta' and 'BR-29', respectively. After the curing process, the activity reduced by 10% in 'BR-29' and increased by 24% in 'Perfecta'. The data demonstrate that effect of the cure depends on the cultivar of onion and that 'Perfecta' presented better results, due to the increase of the antioxidant activity.