The aim of this study was to investigate the effect of drying process variables on the aerodynamic performance and enzymatic activity of a spray-dried model enzyme, Cu,Zn-Superoxide Dismutase (Cu,Zn-SOD). Cu,Zn-SOD is often implicated in a broad spectrum of oxidative stress related diseases, from Cystic Fibrosis to Rheumatoid Arthritis, catalyzing the breakdown of superoxide radicals and so providing the first line of defense against oxygen toxicity. A 23 full factorial experiment was conducted at a constant Drying Gas Flowrate using a trehalose:leucine based composite system previously optimized for dry powder inhalers . Cu,Zn-SOD:trehalose:leucine spray dried powders were successfully generated displaying Fine Particle Fraction values (FPFs) of ≈60% and Enzymatic Activity Retention (EAR) values ranging 50-80%. Aerodynamic performance of these SD powders was mainly affected by Ratom, while enzymatic activity was mainly influenced by Ratom and Ffeed.