Provided are an oral solid preparation composition, including a proton pump inhibitor or a pharmaceutically acceptable salt thereof； and a binding liquid including a basic additive, wherein a content of the basic additive is 2 to 13 parts by weight based on 100 parts by weight of the proton pump inhibitor or a pharmaceutically acceptable salt thereof； an oral solid preparation including the same； and a method of preparing the same. According to the present disclosure, an oral solid preparation exhibiting a significant reduction in the production of related substances and excellent stability against moisture and low pH is provided.
