Abstract:The chemical composition of essential oil isolated by hydro distillation from the aerial parts of Thymus daenensis subsp. daenensis Celak., at different harvest times were determined using Gas Chromatography (GC) and Gas Chromatography/Mass Spectrometry (GC-MS). Twenty six components were identified in Thymus daenensis essential oils. The main components of the oil were thymol (66.62-71.49 %), p-cymene (5.52-7.12 %), β-caryophyllene (3.91-4.09 %), δ-terpinene (3.22-4.3 %) and carvacrol (2.64-2.77 %). The total phenolic content and the antioxidant activity of plant extract was determined by Folin-Ciocalteau and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assays and ferric reducing antioxidant power (FRAP) assay respectively. Total phenols varied from 18.82 to 18.97 (mg GAE/g dw) and the IC 50 in the radical scavenging assay ranged from 8.23 to 8.46 mg/ml and FRAP values ranged form 24.23 to 26.45 μM Quercetin E/g dw. The highest thymol content and radical scavenging effect was found in flowering stage.The essential oil showed 47.89-90.34 % inhibitory properties on Alternaria solani, Fusarium solani and Rhizoctonia solani. The results showed that Flowering stage of harvesting times increased in dry plant weight, and antioxidant activity, and thymol content. Also the oil of T. daenensis has a high antifungal activities against three phathogenic fungi.