This study investigates the effects of wheat flour, wheat starch, and modified starch as cassava starch substitutes, along with their respective amounts, on the physical properties of deep-fried crackers. Additionally, the physical quality of the crackers, including external structure, water activity (aw), bulk density, and hardness, is examined under high relative humidity conditions. Various formulations of crackers were prepared, and their external structure, moisture content, density, and hardness were analyzed. The results revealed that crackers with 15% and 20% wheat flour substitution exhibited smaller and more evenly distributed pores on their surfaces compared to the control formula. Incorporating cross-linked starch led to a smoother surface with smaller and more dispersed air pockets. The wheat flour formula had the highest moisture content and showed a lower density, indicating favorable puffing characteristics. Texture analysis showed that the hardness of all formulations increased over time. The controlled formula exhibited the fastest increase in hardness, indicating that it became firmer and more fracture-resistant. Furthermore, crackers with an aw of 0.15 experienced water migration when exposed to high relative humidity, leading to a transformation from a glassy state to a rubbery state. However, the formulations with wheat flour and cross-linked starch delayed this transformation, maintaining crispiness for an extended period.