Background; Antimicrobial resistance (AMR) poses a critical environmental threat, yet institutional factors shaping frontline stewardship practices remain poorly understood. Nurses occupy a central role in pharmaceutical handling and waste disposal, but evidence on how healthcare systems enable or obstruct the translation of stewardship knowledge into compliant practice is sparse. We investigated whether environmental stewardship failures among frontline nurses in Kazakhstan primarily reflect knowledge deficits or institutional and professional barriers to behavioural translation.Methods: We conducted a parallel convergent mixed-methods study combining a cross-sectional survey of 25,609 nurses across all 20 administrative regions of Kazakhstan with 52 semi-structured interviews in sfindix tertiary hospitals. Multivariable logistic and linear regression models assessed associations between antibiotic disposal training, stewardship knowledge, professional responsibility perceptions, and disposal behaviours. Qualitative thematic analysis explored institutional mechanisms underlying quantitative patterns.Findings: Of 25,609 nurses, 61·9% reported receiving antibiotic disposal training. Awareness of recommended disposal methods (89·6%) and environmental disposal risks (87·6%) was high, yet substantial behavioural gaps persisted. Among nurses with correct disposal knowledge (n=21,064), trained nurses had lower odds of non-compliant behaviour (OR 0·511, 95% CI 0·466–0·560). Employer-integrated training showed the strongest association with compliance (OR 0·368, 95% CI 0·299–0·453), whereas government and NGO training were paradoxically associated with higher odds of non-compliance. Qualitative analysis identified a responsibility gap, professional role silos, fragmented disposal protocols, and reduced frontline visibility of pharmaceutical waste as key barriers.Interpretation: Environmental stewardship failures among nurses reflect institutional barriers to behavioural translation, not knowledge deficits alone. Stewardship responsibilities must be explicitly integrated into nursing roles, reinforced through workplace accountability mechanisms, and embedded within routine clinical workflows. Nurses represent a critical and underutilised resource within One Health AMR containment strategies.