Benralizumab is an anti-eosinophilic monoclonal antibody that reduces exacerbations and improves lung function for patients with severe, uncontrolled asthma with eosinophilic inflammation. We evaluated the impact of baseline factors on benralizumab efficacy for patients with severe asthma.This analysis used pooled data from the SIROCCO (ClinicalTrials.gov identifier NCT01928771) and CALIMA (ClinicalTrials.gov identifier NCT01914757) Phase III studies. Patients aged 12-75 years with severe, uncontrolled asthma receiving high-dosage inhaled corticosteroids plus long-acting β -agonists received benralizumab 30 mg subcutaneously every 8 weeks (Q8W, first three doses every 4 weeks (Q4W)), Q4W or placebo. Baseline factors that influenced benralizumab efficacy were evaluated, including oral corticosteroid (OCS) use, nasal polyposis, pre-bronchodilator forced vital capacity (FVC), prior year exacerbations and age at diagnosis. Efficacy outcomes included annual exacerbation rate and change in pre-bronchodilator forced expiratory volume in 1 s at treatment end relative to placebo.Benralizumab Q8W treatment effect was enhanced with each baseline factor for all patients and those with ≥300 eosinophils·μL relative to the overall population. OCS use, nasal polyposis and FVC <65% of predicted were associated with greater benralizumab Q8W responsiveness for reduced exacerbation rate for patients with <300 eosinophils·μL Baseline clinical factors and blood eosinophil counts can help identify patients potentially responsive to benralizumab.