Arsenic (As) is one of the most harmful pollutants in water bodies which accumulate in animals and bio magnify from lower trophic level to higher trophic level causing imbalance in physiological phenomenon, leading to retarded growth and mortality. Fish is an important resource of healthy protein and poly-unsaturated fatty acids for human diet, it must be free from contaminants and metal toxicants. However, the presence of various metalloids like arsenic in the aquatic environment significantly impart change in the fish meat quality making it unfit for human consumption and overall quantity of fish meat production is affected due to the presence of sufficient amount of arsenic in the water bodies. Therefore, its elimination becomes a global challenge. Moringa oleifera (M. oleifera), a medicinal plant containing several pharmacological properties, was evaluated for ameliorating adverse effects of sub-lethal concentration of arsenic (1/ 3^rd of 96 h LC₅₀ = 6.75 mgL^-1) in Labeo rohita. For this purpose, acclimatized individuals of Labeo rohita were randomly allocated to six experimental glass aquaria in triplicates. The experimental fish were exposed to arsenic alone and in a combination with 2 and 4 % M. oleifera leaves extract for 28 days. Results of current study revealed that immune biomarkers such as total protein, albumin and globulin contents remarkably (p ≤ 0.05) lowered on arsenic exposure. Moreover, upon arsenic exposure red blood cell count (RBC), hemoglobin (Hb), hematocrit (Ht), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) significantly (p ≤ 0.05) decreased, whereas white blood cells (WBC) mean corpuscular volume (MCV) and platelets significantly increased. Conversely, fish treated with 2% or 4% M. oleifera leaf extract showed significant improvement and normalized the immune and hematological alteration in Labeo rohita with respect to time and dose dependent manner. The results of present study thus concluded that arsenic induced immunological and hematological alterations were ameliorated by the M. oleifera leaves extract supplementation. Moreover, 2% or 4% M. oleifera leaf extract supplementation both ameliorate the arsenic induced toxicity but 4% M. oleifera leaf extract supplementation more significantly ameliorate arsenic induced toxic effect.