This study investigates the characteristics of solid propellants with a defoamer. Particularly, this work is an important experiment to confirm the applicability of new raw materials in propellant formulation. The compatibility of a defoamer and oxidizer (AP) showed that the defoamer is suitable as propellant through the differential scanning calorimetry and thermogravimetric analysis. Additionally, the sensitivity test of the propellant with the defoamer was performed. The result indicated normality exists in the impact and friction sensitivity compared with the basic propellant. However, the wet propellant showed an impact sensitivity increase of 175 %. It means that it is very insensitive. When non-silicone defoamer was applied, the viscosity of the propellant with defoamer was excellent, and the initial viscosity of the propellant was reduced by approximately 13 % compared with a basic propellant. Meanwhile, the initial viscosity of the silicone defoamer increased by approximately 42 %. The maximum tensile stress increased by approximately 1.8 %, and the elongation at the maximum tensile stress increased by 9 % when the non-silicone defoamer was applied. However, the maximum tensile stress decreased by approximately 29.1 %, and the elongation at the maximum tensile stress reduced by 7.7 % when the silicone defoamer was applied. Therefore, the non-silicone defoamer was considerably suitable for the propellant.