Objective:To evaluate differences in yield and composition of the essential oil and antioxidant contents in T.diffusa plants from localities in central region of Tamaulipas.Methods:Samples were collected in Tamaulipas,Mexico in the arid zone.Essential oil was obtained through steam distillation and analyzed using GC-MS.Polyphenol contents,antioxidant activities using ABTS and ferric reducing antioxidant power(FRAP) methods also were evaluated.Results:A total of 21 compunds were identified in the essential oils;nevertheless,only Eucalyptol,1,4-Methanocycloocta[d]pyridazine,1,4,4a,5,6,9,10,10a-octahydro-11,11-dimethyl-,(1à,4à,4aà,10aà) y Ethanone,1-(1,3-dimethyl-3-cyclohexen-1-yl) were detected in the three sites.Highest contents were registered in the sample from Padrón y Juárez with phenolic content of 33.85 mg GAE/g of dry material and antioxidant activities with ABTS 72.32% and with FRAP 21.33 mg GAE/g of dry material.Statistical differences were observed in essential oil,phenolics and antioxidants contents between populations.Conclusions:Results suggest that climatic differences and origin influence the phytochemicals in the medicinal plant T.diffusa,and thus,it is worth to consider such effects for industrial and medicinal purposes. Objective: To evaluate differences in yield and composition of the essential oil and antito contents in T.diffusa plants from localities in central region of Tamaulipas.Methods:Samples were collected in Tamaulipas,Mexico in the arid zone.Essential oil was obtained through steam distillation And analyzed using GC-MS.Polyphenol contents, antioxidant activities using ABTS and ferric scaling antioxidant (FRAP) methods also were evaluated.Results:A total of 21 compunds were identified in an essential oils;nevertheless,only Eucalyptol,1,4- Methanocycloocta[d]pyridazine,1,4,4a,5,6,9,10,10a-octahydro-11,11-dimethyl-,(1à,4à,4aà,10aà) y Ethanone,1-(1,3- Dimethyl-3-cyclohexen-1-yl) were detected in the three sites.Highest contents were registered in the sample from Padrón y Juárez with phenolic content of 33.85 mg GAE/g of dry material and antibiotic activities with ABTS 72.32% and with FRAP 21.33 mg GAE/g of dry material.Statistical differences were observed in essential oil,pheno Lics and antioxidants contents between populations.Conclusions:Results suggest that climatic differences and origin influence the phytochemicals in the medicinal plant T.diffusa, and thus,it is worth to consider such effects for industrial and medicinal purposes.