Gelucire 44/14 is a potential and safe absorption enhancer for improving the absorption of poorly absorbable drugs including insulin and calcitonin by pulmonary delivery. It is found that pulmonary absorptions of FD4, FD10 and FD70 are enhanced in different degree by Gelucire 44/14 in a concentration-dependent manner, and the maximal absorption-enhancing effect is obtained when the concentration of Gelucire 44/14 reaches to 2.0% (w/v). It is also found that the absorption enhancing ability of Gelucire Gelucire 44/14 is correlated with the molecular weight of model drugs, and the highest absorption enhancement ratio of Gelucire Gelucire 14/44 is observed when the molecular weight of model drugs reaches to nearly 10000 Da.