Mycotoxins are the chemical substances, produced as the secondary metabolites of some toxigenic species of fungi which cause critical health issues in humans, birds and different animal species while Chlorella vulgaris (CV) is a unicellular microalga which contains plenty of important nutritional ingredients. This study was planned to evaluate the toxicopathological, hematobiochemical and immune changes incurred by dietary supplementation of aflatoxin B1 (AFB1) and their mitigation through CV in broilers. For this study to be conducted, 180 broiler birds of one day old were uniformly distributed into six (06) groups and administered various combinations of AFB1 (200 μg/kg) or CV (0.5 and 1.0%) and the duration of the experiment was 42 days. Parameters deliberated were body weight, feed intake, relative visceral organ weights, gross and histopathological examination, hematological parameters (erythrocytic and leukocytic count, hematocrit and hemoglobin), serum biochemical analysis (serum total proteins, ALT, globulin, albumin, creatinine and urea), humoral response against sheep RBCs, response to subcutaneous injection of phytohemagglutinin-P and phagocytic system function assay. The results of this experiment confirmed that 1.0% CV efficiently mitigated AFB1 induced alterations in the studied parameters while this mitigation was partial when 0.5% CV was used with AFB1. Further studies in this regard are still needed to investigate the exact AFB1:CV ratio responsible for complete amelioration.