Purpose: To formulate salmon calcitonin (sCT)-loaded porous microparticles (PMs) using linear or branched PEG and hydroxyl-propyl beta-cyclodextrin (HPbCD) for pulmonary administration. Methods: Mixtures of linear or branched PEG (10kDa) and HPbCD in different weight ratios were spray dried from water-methanol-butyl acetate solutions. PMs were characterised by thermal analysis, X-ray diffraction, dynamic vapour sorption, inverse gas chromatography and SEM. Particle size distributions were determined by laser diffraction. Aerodynamic properties were measured using a next generation impactor. sCT loading was determined by HPLC. sCT apparent permeability was measured across Calu-3 epithelial monolayers. The bioactivity of sCT was measured using a cAMP assay. sCT pharmacokinetics in Wistar rats were evaluated after i.v. bolus injection of a sCT solution and lung insufflation of the formulations or sCT solution. Results: Particle size distributions showed little change with changes in the HPbCD/PEG ratio, however, particle morphology, surface properties and PEG crystallinity were altered. Increasing the amount of HPbCD above a HPbCD/PEG ratio of 1/1 led to increases in the PMs’ surface roughness, the dispersive contribution of the particles’ surface energy, the water uptake capacity and PEG amorphisation. These changes in particle properties influenced their aerodynamic behaviour. PMs with the highest surface energy and hygroscopicity produced the lowest fine particle fraction and largest MMAD. For all formulations, sCT loading efficiency was around 100%. All formulations containing PEG were able to maintain complete bioactivity of sCT, however, bioactivity decreased to 60% when sCT was processed with HPbCD alone. This formulation demonstrated a significant increase in sCT apparent permeability across Calu-3 monolayer. The relative sCT bioavailability in comparison to the nebulised solution was higher for linear PEG based particles (180%) than for particles made of branched PEG (126%). Conclusion: Using different types of PEG and HPbCD in different proportions allowed microparticles to be formulated with different physicochemical properties leading to different pharmacokinetics profiles of sCT after inhalation. Bioavailability of sCT after lung insufflation of particles was significantly higher than for the pure solution. This work was funded by a Strategic Research Cluster grant (07/SRC/B1154) under the National Development Plan co-funded by EU Structural Funds and Science Foundation Ireland.