Diabetes is considered as the most prevalent metabolic disease. Nannochloropsis oculata is well known by its beneficial values due to the presence of various bioactive compounds. In the present study, Streptozotocin (STZ) induced diabetes resulted in a significant (P<0.05) decrease in all hematological measurements. In addition, it caused significant (P<0.05) elevation in the Lipid Peroxidation Product (LPO) level associated with lowering Total Antioxidant Capacity (TAC) level in the spleen tissue. The N. oculata algal extract restored levels of these measurements to normalcy. The present study revealed that N. oculata contains fat soluble vitamin (β-carotene; 79.069 μg/g) and water soluble vitamins (Vitamin B3, B6 and B12; 3.811, 2.531 and 2.475 μg/g, respectively). Furthermore, it contains various micro and macro minerals (Calcium 20.90% and iron 4924 ppm) in addition to presence of phenolics, chlorophylls and carotenoids. The chromatographic analysis identified presence of flavonoids, pyrogallol (179.65 μg/g) and catachine (46.00 μg/g) in ethyl acetate extract. Also, four phenolic compounds (cinnamic acid, p-comaric acid, p-hydroxy benzoic acid and gallic acid) were isolated and identified by column chromatography. In conclusion, Nannochloropsis oculata algal extract showed scavenging activities against oxidative stress induced by STZ in spleen tissue of diabetic rats.