This research revealed the effect of drying processes on the bioactive properties of marjoram leaves. The total carotenoid content in marjoram leaves ranged between 60.96 µg/g (fresh) and 189.78 µg/g (oven-dried), whereas the total flavonoid content ranged between 949.33 mg CE/100 g (control) and 16,958.59 mg CE/100 g (oven-dried). The total phenolic amounts in marjoram leaves were between 259.17 mg GAE/100 g (fresh) and 1264.17 mg GAE/100 g (oven-dried), while the antioxidant activity values were between 45.23% (fresh) and 77.29% (oven-dried). The 1,2-dihydroxybenzene and (+)-catechin amounts in marjoram leaves were between 19.54 (microwave-dried) and 165.26 (oven-dried) to 20.97 (fresh) and 46.99 mg/100 g (oven-dried), respectively. The kaempferol content in the marjoram plant was specified between 11.45 mg/100 g (fresh) and 43.05 mg/100 g (oven-dried). In general, the quantities of phenolic constituents in the marjoram leaves dried in both drying systems increased compared with fresh samples (except 1,2-dihydroxybenzene, p-coumaric acid, and resveratrol in the microwave-dried samples).