Castella sponge cake was prepared by partially replacing wheat flour with Chungkukjang, a Korean fermented soybean. The physico-chemical, textural and sensory characteristics were then investigated. Specific volume and expansion ratio decreased with increasing Chungkukjang content. The addition of Chungkukjang decreased the moisture content and increased the protein content of castella. Color determination showed addition of Chungkukjang darkened the internal color of castella, probably due to browning caused by the Maillard reaction. Castella with 20 or 30% Chungkukjang had a higher textural hardness than other castellas. A sensory panel perceived that the external and internal color of castella darkened with Chungkukjang substitution. When Chungkukjang was added at or above 20%, castella had a weaker sweet flavor, a stronger roasted flavor, and less lightness and softness than other castellas as perceived by the sensory panels. Up to 30% of the wheat flour could be replaced by Chungkukjang without diminishing acceptability.