The present work deals with the extraction of the essential oil of the Chinese cinnamon Cinnamomum cassia CEO that takes part on the investigation dealing with erythrocyte antioxidant power of Ni SO4 exposed wistar rats during gestation and lactation periods. The extraction by hydrodistillation allowed obtaining an essential oil with a yield of 1%. Furthermore, the phytochemical screening of the crude extract of the plant highlighted the presence of tannins, resins, saponins, terpenoids and flavonoids. The CPG-SM qualitative and quantitative analysis of the CEO has revealed the dominance of cinnamaldehyde (66.54%) and Z-cinnamaldehyde (3.22%). However, the antioxidant activity of CEO essayed in vitro showed a scavenging activity of DPPH free radicals with an IC50 of 83 .54 mg / ml. Besides, the analysis of erythrocyte antioxidant status indicated that Ni significantly increased (p <0.05) the enzymatic activities of both catalase (CAT) and superoxyde dismutase (SOD) and decreased (p <0.05) the enzymatic activity of the glutathione peroxidase (GPx) and the no enzymatic activity of the reduced glutathione (GSH), by involving a dysfunction of the antioxidant defense system. In contrast, the administration of the CEO had contributed significantly on the improvement of enzymatic antioxidant defenses against free radicals resulted from Ni enhanced vulnerability by decreasing significantly (p<0.05) the significant overexpression of both CAT and SOD, and increasing significantly the underexpression (p<0.05) of both GPx and GSH.