This study carried out to investigate the effects of yacon powder on yellow layer cake made with weak flour. After making yellow layer cake with yacon powder, water activity, crumb texture, crumb color, and sensory characteristics were investigated. After 1 day of storage, Aw value of control cake with weak flour did not show any significant differences, whereas those with 2, 4, and 6% yacon powder showed a significant increase in Aw. During storage, the Aw values of yellow layer cakes containing yacon powder decreased. Hardness and gumminess of yellow layer cakes containing yacon powder decreased compared to those of control, whereas springiness and cohesiveness of yellow layer cakes increased compared to those of control. Hardness, springiness, cohesiveness, and gumminess all increased with storage time. Further a higher percentage of yacon powder was associated with lower L and b values as well as a higher a value. The micrographs of yellow layer cakes with yacon powder showed slightly coarser porosity than that of control. The results of the sensory test showed that the overall acceptability of 2% yacon powder cake was the highest.