The study investigates the use of spent coffee (SC), a post-consumer coffee waste, as a stabilizing material in combination with cement (C) for soil improvement. The study explores the influence of different maximum particle sizes of silty sand soil on the resistance behavior when stabilized with cement and various proportions of spent coffee. The substitution ratios used were 0%, 3%, 6%, 9%, and 12% of spent coffee in place of cement. Each replacement ratio was mixed with soils and cement at three different maximum soil sizes (0.6 mm, 2 mm, and 4.25 mm), with an optimum water content and a binder (SC+C) to soil ratio of 0.2. After curing for 14 and 28 days, the unconfined compressive strength (UCS) of the treated soil was tested. The results indicated that samples with up to 6% SC replacement maintained their strength or exhibited slight decreases throughout the curing period. However, at higher replacement ratio, the strength decreased. Additionally, increasing the maximum size of soil particles led to improved strength properties.