This study investigated optimizing the formulation parameters for encapsulation of a model mucinolytic enzyme, -chymotrypsin (-CH), within a novel polymer; poly(ethylene glycol)-co-poly(glycerol adipate-co--pentadecalactone), PEG-co-(PGA-co-PDL) which were then applied to the formulation of DNase I. -CH or DNase I loaded microparticles were prepared via spray drying from double emulsion (w1/o/w2) utilizing chloroform (CHF) as the organic solvent, L-leucine as a dispersibility enhancer and an internal aqueous phase (w1) containing PEG4500 or Pluronic® F-68 (PLF68). -CH released from microparticles was investigated for bioactivity using the azocasein assay and the mucinolytic activity was assessed utilizing the degradation of mucin suspension assay. The chemical structure of PEG-co-(PGA-co-PDL) was characterized by 1H NMR and FT-IR with both analyses confirming PEG incorporated into the polymer backbone, and any unreacted units removed. Optimum formulation -CH-CHF/PLF68, 1% produced the highest bioactivity, enzyme encapsulation (20.083.91%), loading (22.314.34 µg/mg), FPF (fine particle fraction) (37.630.97%); FPD (fine particle dose) (179.889.43 µg), MMAD (mass median aerodynamic diameter) (2.951.61 µm), and the mucinolytic activity was equal to the native non-encapsulated enzyme up to 5 h. DNase I-CHF/PLF68, 1% resulted in enzyme encapsulation (17.443.11%), loading (19.313.27 µg/mg) and activity (81.92.7%). The results indicate PEG-co-(PGA-co-PDL) can be considered as a potential biodegradable polymer carrier for dry powder inhalation of macromolecules for treatment of local pulmonary diseases.