It is an object of the present invention to provide, for a wide range of proteins, an aqueous suspension preparation containing a protein complex that can be concentrated and is high in stability. The present invention is an aqueous suspension preparation comprising an aqueous suspension in which a protein and a polyamino acid that have surface charge in a buffer form a complex to be suspended in the buffer, wherein the protein can be concentrated by removing at least part of water from the complex-containing aqueous suspension, and in the complex, the protein has at least one of shaking stress resistance, fluidity enhancement, oxidation resistance, thermal stability, and aggregation inhibitory properties.
