Polytetrahydrofuran (PTHF) is an effective binder ingredient for improving propellant performance, although it is not an energetic material. PTHF becomes sufficiently rubbery for use as a binder when a triol is added as a crosslinking modifier. In this study, glycerol propoxylate (GPO), with a molecular weight of 1500, was used as a crosslinking modifier, and the curing behavior, tensile properties, and thermal decomposition behaviors of the PTHF binder with GPO were investigated. A PTHF (M-n= 650)/GPO blend with a PTHF/GPO mole ratio (xi) less than or equal to 4 and a PTHF (M-n= 1400)/GPO blend with xi <= 1 were used as propellant binders. The curing behaviors and mechanical properties of the PTHF/GPO blends were influenced by the molecular weight of PTHF and xi, while the thermal decomposition behaviors were not affected. It was found that the PTHF/GPO blends had higher initial viscosity, longer pot life, and unique mechanical properties compared to those of the PTHF blends supplemented with GPO (M-n= 260).