Background: The baseline endotoxin activity (EAT0) may predict the outcome of critically ill septic patients who receive Polymyxin‐B hemadsorption (PMX‐HA), however, the clinical implications of specific EA trends remain unknown. Methods: Subgroup analysis of the prospective, multicenter, observational study EUPHAS2. We included 50 critically ill patients with septic shock and EAT0 ≥ 0.6, who received PMX‐HA. The primary outcome of the study was the EA and SOFA score progression from T0 to 120 h afterwards (T120). Secondary outcomes included the EA and SOFA score progression in whom had EA at 48 h (EAT48) < 0.6 (EA responders, EA‐R) versus who had not (EA non‐responders, EA‐NR). Results: Septic shock was mainly caused by 27 abdominal (54%) and 17 pulmonary (34%) infections, predominantly due to Gram negative bacteria (39 patients, 78%). The SAPS II score was 67.5 [52.8–82.3] and predicted a mortality rate of 75%. Between T0 and T120, the EA decreased (p < 0.001), while the SOFA score and the Inotropic Score (IS) improved (p < 0.001). In comparison with EA‐NR (18 patients, 47%), the EA‐R group (23 patients, 53%) showed faster IS improvement and lower requirement of continuous renal replacement therapy (CRRT) during the ICU stay. Overall hospital mortality occurred in 18 patients (36%). Conclusions: In critically ill patients with septic shock and EAT0 ≥ 0.6 who received PMX‐HA, EA decreased and SOFA score improved over 120 h. In whom high EA resolved within 48 h, IS improvement was faster and CRRT requirement was lower compared with patients with EAT48 ≥ 0.6. [ABSTRACT FROM AUTHOR]